Terminal, base station, transmission method, and reception method

ABSTRACT

A terminal includes: a receiver, which, in operation, receives downlink control information and downlink data; circuitry, which, in operation, determines, based on the downlink control information and an offset, a physical uplink control channel (PUCCH) resource used for transmission of a response signal for the downlink data; and a transmitter, which, in operation, transmits the response signal using the determined PUCCH resource. A first offset is used as the offset when the terminal is configured in a coverage enhancement mode, in which the response signal is allowed to be transmitted repeatedly for one of plural repetition levels in a plurality of subframes, where the first offset is configured for each of the plural repetition levels. The first offset is different from a second offset, which is used when the terminal is not configured in the coverage enhancement mode.

TECHNICAL FIELD

The present disclosure relates to a terminal, a base station, atransmission method, and a reception method.

BACKGROUND ART

3rd Generation Partnership Project Long Term Evolution (3GPP LTE) adoptsOrthogonal Frequency Division Multiple Access (OFDMA) as a downlinkcommunication scheme.

In radio communication systems to which 3GPP LTE is applied, a basestation (hereinafter, may be referred to as “eNB”) transmits asynchronization signal (i.e., Synchronization Channel: SCH) and abroadcast signal (i.e., Physical Broadcast Channel: PBCH) using apredetermined communication resource. Each terminal (hereinafter, may bereferred to as “UE” (User Equipment)) finds the SCH, first and therebyensures synchronization with the base station. Subsequently, theterminal reads BCH information to acquire a base station-specificparameter (e.g., frequency bandwidth) (e.g., see, Non-Patent Literature(hereinafter, abbreviated as “NPL”) 1, 2 and 3).

In addition, upon completion of the acquisition of the basestation-specific parameter, each terminal makes a connection request tothe base station to thereby establish a communication link with the basestation. The base station transmits control information via a controlchannel such as Physical Downlink Control Channel (PDCCH) as appropriateto the terminal with which the communication link has been established.The terminal performs “blind-determination” on each of a plurality ofpieces of control information included in the received PDCCH signal.More specifically, each of the pieces of control information includes aCyclic Redundancy Check (CRC) part and the base station masks this CRCpart using the terminal ID of the transmission target terminal.Accordingly, until the terminal demasks the CRC part of the piece of thereceived control information with its own terminal ID, the terminalcannot determine whether or not the piece of control information isintended for the terminal. In this blind-determination, if the result ofdemasking of the CRC part indicates that the CRC operation is OK, thepiece of control information is determined as being intended for theterminal.

Moreover, in LTE, Hybrid Automatic Repeat Request (HARD) is applied todownlink data to terminals from a base station. More specifically, eachterminal feeds back a response signal indicating the result of errordetection on the downlink data to the base station. Each terminalperforms a CRC on the downlink data and feeds back an Acknowledgment(ACK) when CRC=OK (no error) or Negative Acknowledgment (NACK) whenCRC=Not OK (error) to the base station as a response signal. An uplinkcontrol channel such as Physical Uplink Control Channel (PUCCH) is usedto send the response signal (i.e., ACK/NACK signal) as feedback.

The control information to be transmitted from the base station hereinincludes resource allocation information including information on aresource allocated to the terminal by the base station. As describedabove, PDCCH is used to transmit this control information. This PDCCHincludes one or more L1/L2 control channels (L1/L2 CCH). Each L1/L2 CCHincludes one or more Control Channel Elements (CCE). More specifically,a CCE is the basic unit used to map the control information to PDCCH.Moreover, when a single L1/L2 CCH includes a plurality of CCEs,contiguous CCEs are allocated to the L1/L2 CCH. The base station assignsthe L1/L2 CCH to the resource allocation target terminal in accordancewith the number of CCEs required for indicating the control informationto the resource allocation target terminal. The base station maps thecontrol information to a physical resource corresponding to the CCE ofthe L1/L2 CCH to transmit the control information.

In addition, CCEs are associated with PUCCH component resources(hereinafter, referred to as “PUCCH resource”) in one-to-onecorrespondence. Accordingly, a terminal that has received an L1/L2 CCHidentifies the PUCCH resources corresponding to the CCEs forming theL1/L2 CCH and transmits an ACK/NACK signal to the base station using theidentified PUCCH resources. However, when the L1/L2 CCH occupiescontiguous CCEs, the terminal transmits an ACK/NACK signal to the basestation using one PUCCH resource among the plurality of PUCCH resourcesrespectively corresponding to the CCEs (e.g., PUCCH resourcecorresponding to a CCE having the smallest index).

As illustrated in FIG. 1 , the transmission timing of an ACK/NACK signalon PUCCH from a terminal is in or after a K-th subframe from a subframein which the received PDCCH signal and Physical Downlink Shared Chanel(PDSCH) to which data is assigned by the PDDCH signal are received(i.e., subframe n in FIG. 1 ) (e.g., K=4 in Frequency Division Duplex(FDD) (i.e., subframe n+K in FIG. 1 ).

A plurality of ACK/NACK signals transmitted from a plurality ofterminals are spread using a Zero Auto-correlation (ZAC) sequence havingthe characteristics of zero auto-correlation in time-domain, a Walshsequence and a discrete Fourier transform (DFT) sequence, and arecode-multiplexed in PUCCH as illustrated in FIG. 2 . In FIG. 2 , W(0),W(1), W(2), W(3) represent a length-4 Walsh sequence and F(0), F(1),F(2) represent a length-3 DFT sequence.

As illustrated in FIG. 2 , in the terminals, ACK/NACK signals areprimary-spread over frequency components corresponding to 1Single-Carrier Frequency Division Multiple Access (1SC-FDMA) symbol by aZAC sequence (length-12) on frequency-domain first. In other words, thelength-12 ZAC sequence is multiplied by an ACK/NACK signal componentrepresented by a complex number. Subsequently, the primary-spreadACK/NACK signals and a ZAC sequence serving the reference signals aresecondary-spread using a Walsh sequence (lengh-4: W(0) to W(3)) and aDFT sequence (length-3: F(0) to F(2)). More specifically, each componentof the length-12 sequence signal (i.e., primary-spread ACK/NACK signalsor a ZAC sequence serving as reference signals) is multiplied by eachcomponent of an orthogonal code sequence (i.e., Walsh sequence or DFTsequence). Moreover, the secondary-spread signals are transformed into alength-12 sequence signal in the time-domain by inverse discrete Fouriertransform (IDFT) (or inverse fast Fourier transform (IFFT)). A cyclicprefix (CP) is added to each signal obtained by the IFFT, and a signalof one slot consisting of seven SC-FDMA symbols is thus formed.

PUCCH is mapped to both ends of a system band in the frequency domain.In PUCCH, a radio resource is allocated to each terminal in units ofsubframes. Each subframe consists of two slots, and for PUCCH, frequencyhopping is applied between the first slot and last slot (inter-slotfrequency hopping).

ACK/NACK signals from different terminals are spread using ZAC sequencescorresponding different cyclic shift values (i.e., cyclic shift index)or orthogonal code sequences corresponding to different sequence numbers(i.e., orthogonal cover index (OC index)). An orthogonal code sequenceis a combination of a Walsh sequence and a DFT sequence. In addition,the orthogonal code sequence is referred to as a block-wise spreadingcode in some cases. Thus, base stations can demultiplex thecode-multiplexed ACK/NACK signals, using the conventional despreadingand correlation processing (e.g., see, NPL 4). FIG. 3 illustrates PUCCHresources defined by sequence numbers of orthogonal code sequences (OCindex: 0 to 2) and cyclic shift values (i.e., cyclic shift index: 0 to11) of a ZAC sequence. When a length-4 Walsh sequence and a length-3 DFTsequence are used, a single subcarrier includes a maximum of 36 PUCCHresources (3*12=36). However, it is not always true that the 36 PUCCHresources are all made available. For example, FIG. 3 illustrates a casewhere 18 PUCCH resources (#0 to #17) are made available.

It is worth noting that, as an infrastructure to support the futureinformation society, Machine-to-Machine (M2M) communication, whichenables a service using inter-device autonomous communication withoutinvolving user judgment, has been considered as a promising technologyin recent years. Smart grid is a specific application example of the M2Msystem. Smart grid is an infrastructure system that efficiently suppliesa lifeline such as electricity or gas, performs M2M communicationbetween a smart meter provided in each home or building and a centralserver, and autonomously and efficiently brings supply and demand forresources into balance. Other application examples of the M2Mcommunication system include a monitoring system for goods management orremote medical care, or remote inventory or charge management of vendingmachines.

In the M2M communication system, use of a cellular system supporting abroad range of a communication area is particularly attractingattention. In 3GPP, studies on M2M in the cellular network have beencarried out in LTE and LTE-Advanced standardization under the title of“Machine Type Communication (MTC).” In particular, “CoverageEnhancement,” which further extends the communication area, has beenstudied in order to support a case where an MTC communication device isinstalled at a location not usable in the current communication area,such as a smart meter in the basement of a building (e.g., see NPL 5).

In the MTC coverage enhancement, in particular, a technique called“repetition” that repeatedly transmits the same signal multiple times isconsidered as an important technique for extending the communicationarea. More specifically, repetition transmission is expected to beperformed on channels such as PDCCH, PDSCH, and PUCCH.

CITATION LIST Non-Patent Literature

NPL 1

-   3GPP TS 36.211 V11.5.0, “Physical channels and modulation (Release    11),” December 2013    NPL 2-   3GPP TS 36.212 V11.4.0, “Multiplexing and channel coding (Release    11),” December 2013    NPL 3-   3GPP TS 36.213 V11.5.0, “Physical layer procedures (Release 11),”    December 2013    NPL 4    Seigo Nakao, Tomofumi Takata, Daichi Imamura, and Katsuhiko    Hiramatsu, “Performance enhancement of E-UTRA uplink control channel    in fast fading environments,” Proceeding of 2009 IEEE 69th Vehicular    Technology Conference (VTC2009-Spring), April 2009    NPL 5    3GPP TR 36.888 V12.0.0, “Study on provision of low-cost Machine-Type    Communications (MTC) User Equipments (UEs) based on LTE,” June 2013

SUMMARY OF INVENTION Technical Problem

Studies have not been sufficiently carried out yet on PUCCH resourcesfor transmitting ACK/NACK signals from MTC coverage enhancement modeterminals (i.e., terminals that perform repetition transmission),however. In particular, in a case where an MTC coverage enhancement modeterminal and a normal mode terminal (terminal that does not performrepetition transmission) coexist, the system needs to be designed insuch a way that a PUCCH resource used by the MTC coverage enhancementmode terminal does not collide with a PUCCH resource used by the normalmode terminal.

An aspect of the present disclosure is thus to provide a terminal, abase station, a transmission method, and a reception method that make itpossible to avoid a PUCCH resource collision between the normal modeterminal and MTC coverage enhancement mode terminal without any decreasein the utilization efficiency of PDCCH resources or any increase inscheduling complexity.

Solution to Problem

A terminal according to an aspect of this disclosure includes: areceiving section that receives control information indicatingassignment of downlink data, and the downlink data; a control sectionthat determines a resource used for a response signal for the downlinkdata, based on the control information; and a transmitting section thattransmits the response signal using the determined resource, in which:the transmitting section transmits the response signal using a resourcein a first resource group when the terminal is a first terminal to whichrepetition transmission for the control information, the downlink data,and the response signal is applied; and the transmitting sectiontransmits the response signal using a resource in a second resourcegroup when the terminal is a second terminal to which the repetitiontransmission is not applied, the second resource group being differentfrom the first resource group.

A base station according to an aspect of this disclosure includes: atransmitting section that transmits control information indicatingassignment of downlink data, and the downlink data; a control sectionthat determines a resource used for a response signal for the downlinkdata, based on the control information; and a receiving section thatreceives the response signal using the determined resource, in which:the receiving section receives, using a resource in a first resourcegroup, the response signal transmitted from a first terminal to whichrepetition transmission for the control information, the downlink data,and the response signal is applied; and the receiving section receives,using a resource in a second resource group, the response signaltransmitted from a second terminal to which the repetition transmissionis not applied, the second resource group being different from the firstresource group.

A transmitting method according to an aspect of this disclosureincludes: receiving control information indicating assignment ofdownlink data, and the downlink data; determining a resource used for aresponse signal for the downlink data, based on the control information;and transmitting the response signal using the determined resource, inwhich: in the transmitting of the response signal, the response signalis transmitted using a resource in a first resource group from a firstterminal to which repetition transmission for the control information,the downlink data, and the response signal is applied; and in thetransmitting of the response signal, the response signal is transmittedusing a resource in a second resource group from a second terminal towhich the repetition transmission is not applied, the second resourcegroup being different from the first resource group.

A receiving method according to an aspect of this disclosure includes:transmitting control information indicating assignment of downlink data,and the downlink data; determining a resource used for a response signalfor the downlink data, based on the control information; and receivingthe response signal using the determined resource, in which: in thereceiving of the response signal, the response signal transmitted from afirst terminal is received using a resource in a first resource group,the first terminal being a terminal to which repetition transmission forthe control information, the downlink data, and the response signal isapplied; and in the receiving of the response signal, the responsesignal transmitted from a second terminal is received using a resourcein a second resource group that is different from the first resourcegroup, the second terminal being a terminal to which the repetitiontransmission is not applied.

Advantageous Effects of Invention

According to an aspect of the present disclosure, it is possible toavoid a PUCCH resource collision between the normal mode terminal andMTC coverage enhancement mode terminal without any decrease in theutilization efficiency of PDCCH resources or any increase in schedulingcomplexity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the transmission timing of eachchannel;

FIG. 2 is a diagram illustrating a method of spreading response signalsand reference signals;

FIG. 3 is a diagram illustrating an example of PUCCH resources;

FIG. 4 is a diagram illustrating the transmission timing of each channelduring repetition transmission;

FIG. 5 is a block diagram illustrating an example of a PUCCH resourcecollision;

FIG. 6 is a block diagram illustrating a primary configuration of a basestation according to Embodiment 1;

FIG. 7 is a block diagram illustrating a primary configuration of aterminal according to Embodiment 1;

FIG. 8 is a block diagram illustrating a configuration of the basestation according to Embodiment 1;

FIG. 9 is a block diagram illustrating a configuration of the terminalaccording to Embodiment 1;

FIG. 10 is a diagram illustrating PUCCH resources according toEmbodiment 1;

FIG. 11 is a diagram illustrating PUCCH resources according toEmbodiment 2;

FIG. 12 is a diagram illustrating PUCCH resources according toEmbodiment 3;

FIG. 13 is a diagram illustrating an association between CCEs and PUCCHresources according to Embodiment 4;

FIG. 14 is a diagram illustrating an association between CCEs and PUCCHresources according to Embodiment 4;

FIG. 15 is a diagram illustrating an example of a PUCCH resourcecollision according to Embodiment 5;

FIG. 16 is a diagram illustrating the transmission timing of eachchannel according to Embodiment 5;

FIG. 17 is a diagram illustrating an example of a PUCCH resourcecollision according to Embodiment 6; and

FIG. 18 is a diagram illustrating the transmission timing of eachchannel according to Embodiment 6.

DESCRIPTION OF EMBODIMENTS

FIG. 4 illustrates the transmission timing of each channel in MTCcoverage enhancement that is assumed to be an aspect of this disclosure.In FIG. 4 , “N_(PDCCH),” “N_(PDSCH),” and “N_(PUCCH)” represent therepetition level (the number of repetitions, or repetition factor) ofPDCCH, the repetition level of PDSCH, and the repetition level of PUCCH,respectively. As illustrated in FIG. 4 , the repetition transmission ofPDCCH is performed first, and then, the repetition of PDSCH to whichdata is assigned by the PDCCH is performed in MTC coverage enhancement.The transmission timing of an ACK/NACK signal (PUCCH) from the terminalis after K_(MTC) subframes which follow the subframe in which thereception of PDSCH has ended.

In a case where an MTC coverage enhancement mode terminal (terminal thatperforms repetition transmission) and a normal mode terminal (terminalthat does not perform repetition transmission) coexist in a coveragearea formed by the same base station, setting of different controlchannels for downlink control signals to the respective terminals causesa decrease in the spectral efficiency. In order to avoid such adecrease, it is possible to set a downlink control channel (PDCCH) usingthe same frequency for the normal mode and MTC coverage enhancement modeterminals.

With this setting, the time interval between a subframe in which anACK/NACK signal is transmitted (first subframe in which repetitiontransmission of PUCCH is performed) and a subframe in which PDCCHincluding a CCE associated with the PUCCH resource used for transmissionof an ACK/NACK signal is transmitted (last subframe in which repetitiontransmission of PDCCH is performed) varies between the normal mode andMTC coverage enhancement mode terminals. For this reason, when both ofthe terminals transmit an ACK/NACK signal in the same subframe, the CCEnumber associated with the PUCCH resource on which the normal modeterminal transmits the ACK/NACK signal and the CCE number associatedwith the PUCCH resource on which the MTC coverage enhancement terminaltransmits the ACK/NACK signal may overlap each other. In this case, theACK/NACK signals are transmitted using the same PUCCH resource by bothof the terminals.

FIG. 5 illustrates an example of the case where the PUCCH resource usedby the normal mode terminal and the PUCCH resource used by the MTCcoverage enhancement mode terminal collide with each other. In FIG. 5 ,“n” represents the subframe where the PUCCH resource collision occurs.

In this case, PDCCH for the normal mode terminal is transmitted insubframe n−K, and the PDSCH assigned by the PDCCH is transmitted also insubframe n−K. Meanwhile, for the MTC coverage enhancement mode terminal,PDCCH is transmitted in subframe n−K_(MTC)−N_(PDSCH)−N_(PDCCH) ton−K_(MTC)−N_(PDSCH)−1. The PDSCH assigned by the PDCCH is transmitted insubframe n−K_(MTC)−N_(PDSCH) to n−K_(MTC)−1.

When the subframe in which PDCCH is transmitted to the normal modeterminal overlaps the subframe in which PDCCH is transmitted to the MTCcoverage enhancement mode terminal, scheduling is performed so as toprevent transmission of PDCCH to both of the terminals using the sameCCE. However, other than this case (e.g., in FIG. 5 ), the same CCE canbe used for PDCCH transmission to the normal mode terminal and forrepetition transmission of PDCCH to the MTC coverage enhancement modeterminal. For example, CCE #0 to CCE #3 are used for transmission ofPDCCH to the MTC coverage enhancement mode terminal, and this MTCcoverage enhancement mode terminal uses the PUCCH resource correspondingto CCE #0 (the smallest index of CCE #0 to CCE #3). In FIG. 5 , CCE #0and CCE #1 are used for transmission of PDCCH to the normal modeterminal, and this normal mode terminal uses a PUCCH resourcecorresponding to CCE #0 (the smallest index of CCE #0 and CCE #1).

As a result, a PUCCH resource collision in transmission of ACK/NACKsignals occurs from the normal mode terminal and MTC coverageenhancement mode terminal.

In order to avoid a case where a PUCCH resource for transmitting anACK/NACK signal from the normal mode terminal collides with a PUCCHresource for transmitting an ACK/NACK signal from the MTC coverageenhancement mode terminal, the base station may control PDCCH assignmentfor the normal mode terminal (i.e., not to allocate, to the normal modeterminal, a CCE that has been used for the MTC coverage enhancement modeterminal in the previous subframes). This case, however, involves aproblem in that the utilization efficiency of PDCCH resources decreasesor that scheduling complexity increases.

Hereinafter, a description will be given of each embodiment of thepresent disclosure in detail with reference to the accompanyingdrawings.

[Overview of Communication System]

In the following description, a Frequency Division Duplex (FDD) systemwill be used as an example.

In addition, a communication system according to each embodiment of thisdisclosure is an LTE-Advanced compliant system, for example, andincludes base station 100 and terminal 200.

Terminal 200 is configured with a normal mode or an MTC coverageenhancement mode. When terminal 200 is configured with the MTC coverageenhancement mode, for example, repetition transmission for transmissionof PDCCH, PDSCH, or PUCCH is applied to terminal 200 over a plurality ofsubframes. More specifically, terminal 200 repeatedly transmits the samesignal over subframes that are contiguous for a predetermined repetitionlevel.

FIG. 6 is a block diagram illustrating a primary configuration of basestation 100 according to Embodiment 1 of this disclosure. In basestation 100 illustrated in FIG. 6 , transmission section 112 transmitscontrol information indicating downlink data assignment (PDCCH signal)and downlink data (PDSCH signal), and control section 101 determines aresource used for an ACK/NACK signal for the downlink data, based on thecontrol information mentioned above, and an ACK/NACK signal receivingsection (PUCCH extracting section 116, despreading section 118, andcorrelation processing section 119) receives an ACK/NACK signal usingthe determined resource. Note that, this receiving section receives,using a resource in a first resource group (PUCCH resource region), anACK/NACK signal transmitted from a first terminal to which repetitiontransmission for the control information, downlink data and ACK/NACKsignal is applied, and receives, using a resource in a second resourcegroup (PUCCH resource region) that is different from the first resourcegroup, an ACK/NACK signal transmitted from a second terminal to whichthe repetition transmission is not applied.

FIG. 7 is a block diagram illustrating a primary configuration ofterminal 200 according to each embodiment of this disclosure. Interminal 200 illustrated in FIG. 7 , receiving section 202 receivescontrol information indicating downlink data assignment, and downlinkdata. In addition, control section 213 determines a resource used for anACK/NACK signal for the downlink data, based on the control information,and an ACK/NACK signal transmission section (primary-spreading section216, secondary-spreading section 217, IFFT section 218) transmits theACK/NACK signal using the determined resource. Note that, when theterminal including the ACK/NACK signal transmission section is a firstterminal to which repetition transmission for the control information,downlink data and ACK/NACK signal is applied, the ACK/NACK signaltransmission section transmits the ACK/NACK signal using a resource in afirst resource group. When the terminal including the ACK/NACK signaltransmission section is a second terminal to which the repetitiontransmission is not applied, the ACK/NACK signal transmission sectiontransmits the ACK/NACK signal using a resource in a second resourcegroup that is different from the first resource group.

Embodiment 1

[Configuration of Base Station]

FIG. 8 is a block diagram illustrating a configuration of base station100 according to Embodiment 1 of the present disclosure. In FIG. 8 ,base station 100 includes control section 101, control signal generatingsection 102, control signal coding section 103, control signalmodulation section 104, broadcast signal generating section 105, datacoding section 106, retransmission control section 107, data modulationsection 108, signal assignment section 109, inverse fast Fouriertransform (IFFT) section 110, CP adding section 111, transmissionsection 112, antenna 113, receiving section 114, CP removing section115, PUCCH extracting section 116, sequence controlling section 117,despreading section 118, correlation processing section 119, anddetermination section 120.

Control section 101 allocates a downlink resource for transmittingcontrol information (downlink control information assignment resource),and a downlink resource for transmitting downlink data (transmissiondata) (downlink data assignment resource) to resource allocation targetterminal 200. The downlink control information assignment resource isselected within resources corresponding to PDCCH or Enhanced PDCCH(EPDCCH). In addition, the downlink data assignment resource is selectedwithin resources corresponding to PDSCH. When a plurality of resourceallocation target terminals 200 are present within the same subframe,control section 101 allocates a different resource to each resourceallocation target terminal 200. The downlink control informationassignment resource is equivalent to the L1/L2 CCH described above.Stated differently, the downlink control information assignment resourceincludes one or a plurality of CCEs. In addition, as described above,when PUCCH is implicitly indicated using a CCE, each CCE is associatedwith a PUCCH resource of an uplink control channel region (PUCCHregion).

Control section 101 identifies a PUCCH resource corresponding to a CCEoccupied by PDCCH including the control information (i.e., frequency,and code using in primary-spreading/secondary-spreading). Controlsection 101 outputs, to sequence control section 117, information on aZAC sequence and orthogonal code sequence that may be used for spreadinga PUCCH signal transmitted from terminal 200 (ACK/NACK signals andreference signals) (i.e., information on PUCCH resource), and outputsinformation on the frequency to PUCCH extracting section 116.

Moreover, control section 101 determines a coding rate used fortransmitting control information to resource allocation target terminal200 and outputs the determined coding rate to control signal codingsection 103. Control section 101 also determines a coding rate used fortransmitting downlink data to resource allocation target terminal 200and outputs the determined coding rate to data coding section 106.

Note that, the data volume of control information varies depending onthe determined coding rate, so that control section 101 allocatesdownlink control information assignment resource including CCEssufficient for mapping the control information of this data volume.Control section 101 outputs information on a downlink data assignmentresource to control signal generating section 102. Control section 101outputs information on the downlink data assignment resource anddownlink control information assignment resource to signal assignmentsection 109.

Moreover, when resource allocation target terminal 200 is configuredwith the MTC coverage enhancement mode, control section 101 outputsinformation on the repetition level (the number of repetitions) for eachchannel (PDCCH, PDSCH, or PUCCH) of resource allocation target terminal200 to control signal generating section 102 and data coding section106.

Moreover, control section 101 instructs broadcast signal generatingsection 105 to generate a broadcast signal based on a parameterdetermined for each base station in advance.

Control section 101 also generates information on PUCCH resources andoutputs the information to control signal generating section 102. Theinformation on PUCCH resources includes a parameter for identifying thePUCCH resources used in the normal mode terminal and MTC coverageenhancement mode terminal. Note that, the information on PUCCH resourcesmay be indicated to terminals 200 as broadcast information indicating acell-specific value, and may be indicated to terminals 200 by higherlayer signaling.

Control signal generating section 102 generates a control signal usingthe information received from control section 101 (i.e., information ondownlink data assignment resource, information on repetition level ofPUCCH, or information PUCCH resources) and outputs the control signal tocontrol signal coding section 103. When a plurality of resourceallocation target terminals 200 are present, the control signal includesa terminal ID of each destination terminal for the purpose ofidentifying each resource allocation target terminal 200. For example,the control signal includes CRC bits masked by the terminal IDs ofdestination terminals. When resource allocation target terminal 200 isconfigured with the MTC coverage enhancement mode, control signalgenerating section 102 generates a repetition signal in accordance withthe information on the repetition level received from control section101. More specifically, when the repetition level of PDCCH is greaterthan 1, control signal generating section 102 outputs the same controlsignal over a plurality of contiguous subframes corresponding to therepetition level to control signal coding section 103.

Control signal coding section 103 encodes the control signal receivedfrom control signal generating section 102, in accordance with thecoding rate received from control section 101, and outputs the codedcontrol signal to control signal modulation section 104.

Control signal modulation section 104 modulates the control signalreceived from control signal coding section 103 and outputs themodulated control signal to signal assignment section 109.

Broadcast signal generating section 105 generates a broadcast signal inaccordance with an instruction from control section 101 and outputs thebroadcast signal to signal assignment section 109. Note that, thebroadcast signal includes a signal for system bandwidth, or PUCCHresources, for example. The broadcast signal may be subjected to codingprocessing and modulation processing.

Data coding section 106 encodes transmission data for each destinationterminal (bit sequence, i.e., downlink data) in accordance with thecoding rate received from control section 101 and outputs the coded datasignal to retransmission control section 107. Moreover, when resourceallocation target terminal 200 is configured with the MTC coverageenhancement mode, data coding section 106 generates a repetition signalin accordance with the information on the repetition level received fromcontrol section 101. More specifically, when the repetition level ofPDSCH is greater than 1, data coding section 106 outputs the same datasignal to retransmission control section 107 over a plurality ofcontiguous subframes corresponding to the repetition level.

Retransmission control section 107 holds the coded data signal receivedfrom data coding section 106 and also outputs the coded data signal todata modulation section 108 for the initial transmission. Retransmissioncontrol section 107 holds the coded data signal for each destinationterminal. In addition, upon reception of a NACK for the transmitted datasignal from determination section 120 to be described hereinafter,retransmission control section 107 outputs the corresponding held datato data modulation section 108. Upon reception of an ACK for thetransmitted data signal, retransmission control section 107 deletes thecorresponding held data.

Data modulation section 108 modulates a data signal received fromretransmission control section 107 and outputs the data modulationsignal to signal assignment section 109.

Signal assignment section 109 maps the control signal received fromcontrol signal modulation section 104, the broadcast signal receivedfrom broadcast signal generating section 105, and the data modulationsignal received from data modulation section 108 to downlink resources(such as downlink data signal assignment resources or downlink controlinformation assignment resources) and outputs the mapped signals to IFFTsection 110. More specifically, signal assignment section 109 maps thecontrol signal to a resource indicated by the downlink controlinformation assignment resource received from control section 101 andalso maps the data modulation signal to a resource indicated by thedownlink data assignment resource received from control section 101.Moreover, signal assignment section 109 maps the broadcast signal to apreviously set time and frequency resource.

IFFT section 110 transforms a frequency domain signal into a time domainsignal by performing IFFT processing on the signal received from signalassignment section 109. IFFT section 110 outputs the time domain signalto CP adding section 111.

CP adding section 111 adds a CP to the signal received from IFFT section110 and outputs the CP added signal (OFDM signal) to transmissionsection 112.

Transmission section 112 performs radio frequency (RF) processing suchas digital to analog (D/A) conversion or up-conversion on the OFDMsignal received from CP adding section 111 and outputs a radio signal toterminal 200 via antenna 113.

Receiving section 114 performs RF processing such as down-conversion oranalog-to-digital (A/D) conversion on the radio signal received fromterminal 200 via antenna 113 and outputs a received signal thus obtainedto CP removal section 115.

CP removal section 115 removes a CP added to the received signal to bereceived from receiving section 114 and outputs the CP removed signal toPUCCH extracting section 116.

PUCCH extracting section 116 extracts an uplink control channel signal(PUCCH) received from CP removal section 115 based on the informationreceived from control section 101 and outputs the extracted PUCCH todespreading section 118. When an MTC coverage enhancement mode terminal200 is present, PUCCH extracting section 116 performs coherent combiningon the PUCCH repeatedly transmitted over a plurality of subframes toextract the PUCCH (combined signal).

Sequence control section 117 generates a ZAC sequence and orthogonalcode sequence that may be used for spreading ACK/NACK signals andreference signals transmitted from terminal 200, based on theinformation on the ZAC sequence and orthogonal code sequence receivedfrom control section 101. Sequence control section 117 outputs theorthogonal code sequence to despreading section 118 and also outputs theZAC sequence to correlation processing section 119.

Despreading section 118 despreads a portion of the signal received fromPUCCH extracting section 116 that is a signal portion corresponding tothe ACK/NACK signal, using the orthogonal code sequence received fromsequence control section 117 (i.e., orthogonal code sequence used insecondary-spreading by terminal 200), and outputs the despread signal tocorrelation processing section 119.

Correlation processing section 119 obtains a correlation value betweenthe ZAC sequence received as input from sequence control section 117(i.e., ZAC sequence that may be used in primary-spreading by terminal200) and the signal received as input from despreading section 118, andoutputs the obtained correlation value to determination section 120.

Determination section 120 determines whether the ACK/NACK signaltransmitted from terminal 200 indicates an ACK or NACK for thetransmitted data, based on the correlation value received fromcorrelation processing section 119. Determination section 120 outputsthe result of determination to retransmission control section 107.

[Configuration of Terminal]

FIG. 9 is a block diagram illustrating a configuration of terminal 200according to Embodiment 1 of the present disclosure. In FIG. 9 ,terminal 200 includes antenna 201, receiving section 202, CP removingsection 203, fast Fourier transform (FFT) section 204, extractionsection 205, broadcast signal receiving section 206, control signaldemodulation section 207, control signal decoding section 208,determination section 209, data demodulation section 210, data decodingsection 211, CRC section 212, control section 213, ACK/NACK generatingsection 214, modulation section 215, primary-spreading section 216,secondary-spreading section 217, IFFT section 218, CP adding section219, and transmitting section 220.

Receiving section 202 performs RF processing such as down-conversion orA/D conversion on the radio signal received from base station 100 viaantenna 201 to obtain a baseband OFDM signal. Receiving section 202outputs the OFDM signal to CP removing section 203.

CP removing section 203 removes the CP added to the OFDM signal receivedfrom receiving section 202 and outputs the signal after the CP removalto FFT section 204.

FFT section 204 performs FFT processing on the signal received from CPremoving section 203 to transform a time domain signal into a frequencydomain signal. FFT section 204 outputs the frequency domain signal toextraction section 205.

Extraction section 205 extracts a broadcast signal from the signalreceived from FFT section 204 and outputs the broadcast signal tobroadcast signal receiving section 206. Note that, a resource to whichthe broadcast signal is mapped is determined in advance, so thatextraction section 205 obtains the broadcast signal by extractinginformation mapped to the resource. The extracted broadcast signalincludes a signal related to a system bandwidth or a PUCCH resource, forexample.

In addition, extraction section 205 extracts a downlink control channelsignal (PDCCH signal) from the signal received from FFT section 204 andoutputs the downlink control channel signal to control signaldemodulation section 207. Furthermore, extraction section 205 extractsdownlink data (PDSCH signal) from the signal received from FFT section204, based on the information on the downlink data assignment resourceintended for terminal 200 of extraction section 205 received fromdetermination section 209, and outputs the downlink data to datademodulation section 210. The PDCCH signal includes the information onthe downlink data assignment resource, the information on the repetitionlevel of PUCCH, or the information on PUCCH resources, for example.

Moreover, when terminal 200 is configured with the MTC coverageenhancement mode, and the PDCCH signal is repeatedly transmitted,extraction section 205 performs coherent combining on the PDCCHrepeatedly transmitted over a plurality of subframes to extract thePDCCH. Likewise, when downlink data (PDSCH signal) is repeatedlytransmitted, extraction section 205 performs coherent combining on thePDSCH repeatedly transmitted over a plurality of subframes to extractthe downlink data.

Broadcast signal receiving section 206 obtains information on the systembandwidth or PUCCH resources from the broadcast signal received fromextraction section 205. When the broadcast signal has been subjected tocoding processing and modulation processing, broadcast signal receivingsection 206 performs demodulation processing and decoding processing onthe broadcast signal. Broadcast signal receiving section 206 outputs theobtained broadcast signal to determination section 209 or controlsection 213.

Control signal demodulation section 207 demodulates the PDCCH signalreceived from extraction section 205 and outputs the demodulated PDCCHsignal to control signal decoding section 208.

Control signal decoding section 208 decodes the PDCCH signal receivedfrom control signal demodulation section 207 and outputs the decodingresult to determination section 209.

Determination section 209 performs blind-determination to find outwhether or not the control information included in the decoding resultreceived from control signal decoding section 208 is the controlinformation intended for terminal 200. For example, determinationsection 209 perform de-masking on the CRC bits by the terminal ID ofterminal 200 and determines that the control information resulting inCRC=OK (no error) as the control information intended for terminal 200.Determination section 209 outputs information on the downlink dataassignment resource included in the control information intended forterminal 200 to extraction section 205. Moreover, determination section209 identifies a CCE to which the control information intended forterminal 200 is mapped, and outputs the identification information ofthe identified CCE to control section 213.

Data demodulation section 210 demodulates the downlink data receivedfrom extraction section 205 and outputs the demodulated downlink data todata decoding section 211.

Data decoding section 211 decodes the downlink data received from datademodulation section 210 and outputs the decoded downlink data to CRCsection 212.

CRC section 212 performs CRC error detection on the downlink datareceived from data decoding section 211 and outputs the error detectionresult to ACK/NACK generating section 214. In addition, CRC section 212transmits, as the received data, the downlink data that has beendetermined as having no error as a result of error detection.

Control section 213 holds in advance the information on a PUCCH resourceindicated to terminal 200 via a broadcast signal, PDCCH signal or higherlayer signaling, and the information on the repetition level.

Control section 213 uses the information on a PUCCH resource and CCEidentification information received from determination section 209 andthereby identifies a PUCCH resource corresponding to the CCE indicatedby the CCE identification information (i.e., frequency, and code used inprimary-spreading/secondary-spreading). Stated differently, controlsection 213 identifies a PUCCH resource on the uplink control channelbased on the CCE identification information.

More specifically, control section 213 generates a ZAC sequencecorresponding to a PUCCH resource to be used and also determines acyclic shift value to be used, based on the configured cyclic shiftvalue and outputs the ZAC sequence and cyclic shift value toprimary-spreading section 216. In addition, control section 213 outputsan orthogonal code sequence corresponding to the PUCCH resource to beused to secondary-spreading section 217. Control section 213 outputs thefrequency resource (subcarriers) corresponding to the PUCCH resource tobe used to IFFT section 218.

Moreover, when terminal 200 is configured with the MTC coverageenhancement mode, control section 213 outputs the information on therepetition level of PUCCH to ACK/NACK generating section 214.

ACK/NACK generating section 214 generates an ACK/NACK signal based onthe error detection result received from CRC section 212. Morespecifically, ACK/NACK generating section 214 generates a NACK signalwhen an error is detected, and generates an ACK signal when no error isdetected. ACK/NACK generating section 214 outputs the generated ACK/NACKsignal to modulation section 215. When the terminal including ACK/NACKgenerating section 214 is configured with the MTC coverage enhancementmode, ACK/NACK generating section 214 transmits a repetition signal inaccordance with the information on the repetition level received fromcontrol section 213. More specifically, ACK/NACK generating section 214outputs the same ACK/NACK signal to modulation section 215 over aplurality of contiguous subframes corresponding to the repetition level.

Modulation section 215 modulates an ACK/NACK signal received fromACK/NACK generating section 214 and outputs the modulated ACK/NACKsignal to primary-spreading section 216.

Primary-spreading section 216 performs primary-spreading of thereference signal, and ACK/NACK signal received from modulation section215, using the ZAC sequence and cyclic shift value configured by controlsection 213, and outputs the ACK/NACK signal and reference signal afterthe primary-spreading to secondary-spreading section 217.

Secondary-spreading section 217 performs secondary-spreading of theACK/NACK signal and reference signal using the orthogonal code sequenceconfigured by control section 213 and outputs the signal after thesecondary-spreading to IFFT section 218.

IFFT section 218 generates a time domain signal by mapping the ACK/NACKsignal and reference signal received from secondary-spreading section217 to the subcarriers and performing IFFT processing, using thefrequency resource configured by control section 213. IFFT section 218outputs the generated signal to CP adding section 219.

CP adding section 219 adds a CP to the signal received from IFFT section218 and transmits the CP added signal to transmission section 220.

Transmission section 220 performs RF processing such as D/A conversionor up-conversion on the signal received from CP adding section 219 andtransmits the radio signal to base station 100 via antenna 201.

[Operation of Base Station 100 and Terminal 200]

Hereinafter, a description will be given of operation of base station100 and terminal 200 configured in the manner described above.

Hereinafter, a case where a normal mode terminal and an MTC coverageenhancement mode terminal coexist in a cell formed by base station 100will be described.

Base station 100 according to Embodiment 1 indicates information on aPUCCH resource to each terminal 200 in advance. The information on aPUCCH resource is information on an offset value used for identifying aPUCCH resource number from a CCE number and a maximum number of PUCCHresources to be code-multiplexed per resource block (RB) placed in eachPUCCH region.

In Embodiment 1, the offset value mentioned above is independentlyconfigured for the normal mode terminal and the MTC coverage enhancementmode terminal.

More specifically, upon reception of downlink assignment controlinformation (PDCCH or EPDCCH), the normal mode terminal determinesresource number n_(PUCCH) of a PUCCH resource for transmitting anACK/NACK signal for downlink data (PDSCH) indicated by the correspondingassignment control information, using the following equation.n _(PUCCH) =n _(CCE) +N _(PUCCH) ⁽¹⁾  (Equation 1)

In Equation 1, “n_(CCE)” represents the CCE number of a CCE occupied byPDCCH (integer equal to or greater than 0). More specifically, whenPDCCH occupies only one CCE, “n_(CCE)” represents the CCE number of theCCE. Meanwhile, when PDCCH occupies a plurality of CCEs, “n_(CCE)”represents the smallest CCE number.

In Equation 1, “N_(PUCCH) ⁽¹⁾” represents the offset value foridentifying a PUCCH resource number from a CCE number. For example, in3GPP Release 11, N_(PUCCH) ⁽¹⁾ represents the number of PUCCH resourcesreserved for Semi-Persistent Scheduling/Scheduling Request (SPS/SR)resources. “N_(PUCCH) ⁽¹⁾” is a common value in the cell, for example,and is indicated to terminal 200 from base station 100 by a broadcastsignal or higher layer signaling.

The normal mode terminal determines an OC index and cyclic shift valueto be actually used, based on the determined PUCCH resource number“n_(PUCCH).”

Meanwhile, upon reception of downlink assignment control information(PDCCH or EPDCCH), the MTC coverage enhancement mode terminal determinesresource number “n_(PUCCH_MTC)” of a PUCCH resource for transmitting anACK/NACK signal for downlink data (PDSCH) indicated by the correspondingassignment control information, using the following equation.n _(PUCCH_MTC) =n _(CCE) +N _(PUCCH_MTC) ⁽¹⁾  (Equation 2)

In Equation 2, “N_(PUCCH_MTC) ⁽¹⁾” represents an offset value foridentifying a PUCCH resource number from a CCE number for the MTCcoverage enhancement mode terminal.

More specifically, an independent offset value, N_(PUCCH_MTC) ⁽¹⁾, whichis different from offset value N_(PUCCH) ⁽¹⁾ for the normal modeterminal, is configured for the MTC coverage enhancement mode terminal.For example, N_(PUCCH_MTC) ⁽¹⁾ may be an individual (UE-specific) valuedependent on terminal 200, or may be value common to the MTC coverageenhancement mode terminals.

The MTC coverage enhancement mode terminal determines an OC index andcyclic shift value to be actually used, based on the determined PUCCHresource number “n_(PUCCH_MTC).”

FIG. 10 illustrates an example of PUCCH resources for the normal modeterminal and MTC coverage enhancement mode terminal.

In FIG. 10 , 18 PUCCH resources are available among a maximum of 36PUCCH resources for each RB (Physical RB (PRB)) as in the case of FIG. 3. In FIG. 10 , 54 available PUCCH resources are assigned PUCCH resourcenumbers (#0 to #53), respectively, over three RBs.

In FIG. 10 , offset value “N_(PUCCH) ⁽¹⁾” for the normal mode terminalis equal to 6, and offset value “N_(PUCCH_MTC) ⁽¹⁾” for the MTC coverageenhancement mode terminal is equal to 30.

More specifically, the normal mode terminal transmits an ACK/NACK signalusing a PUCCH resource of PUCCH resource number “n_(PUCCH)=n_(CCE)+6.”Meanwhile, the MTC coverage enhancement mode terminal transmits anACK/NACK signal using a PUCCH resource of PUCCH resource number“n_(PUCCH_MTC)=n_(CCE)+30.”

Stated differently, when configured with the normal mode, terminal 200transmits an ACK/NACK signal using a PUCCH resource in a PUCCH resourcegroup for the normal mode terminals, and when configured with the MTCcoverage enhancement mode, terminal 200 transmits an ACK/NACK signalusing a PUCCH resource in a PUCCH resource group for the MTC coverageenhancement terminals, which is different from the PUCCH resource groupfor the normal mode terminals.

Likewise, base station 100 receives an ACK/NACK signal transmitted fromthe normal mode terminal, using a resource in the PUCCH resource groupfor the normal mode terminals, and receives an ACK/NACK signaltransmitted from the MTC coverage enhancement mode terminal, using aresource in the PUCCH resource group for the MTC coverage enhancementmode terminals, which is different from the PUCCH resource group for thenormal mode terminals.

In this way, as illustrated in FIG. 10 , the PUCCH resource groupavailable for transmission of an ACK/NACK signal from the MTC coverageenhancement mode terminal to which repetition transmission for a PDCCHsignal, PDSCH signal, and ACK/NACK signal is applied is different fromthe PUCCH resource group available for transmission of an ACK/NACKsignal from the normal mode terminal to which the repetitiontransmission is not applied. Stated differently, the PUCCH resourceregion is divided into a region for the normal mode terminals and aregion for the MTC coverage enhancement mode terminals by settingmutually different offset values for the normal mode and MTC coverageenhancement mode terminals, each of the offset values being used foridentifying a PUCCH resource number from a CCE number.

Note that, FIG. 10 illustrates a case where the number of CCEs availablefor terminals 200 of each mode is 24. The number of CCEs available forterminals 200 of each mode is, however, not limited to 24, and may takeanother value. More specifically, offset values “N_(PUCCH) ⁽¹⁾” and“N_(PUCCH_MTC) ⁽¹⁾” may be set in such a way that the PUCCH resourceregion is divided into regions for terminals 200 of the respectivemodes, depending on the number of available CCEs.

Hereinafter, a description will be given of a case where the CCE numbercorresponding to the PUCCH resource used for an ACK/NACK signaltransmitted in the same subframe is CCE #0 (i.e., n_(CCE)=0) asillustrated in FIG. 5 , for example.

In this case, the normal mode terminal uses a PUCCH resourcecorresponding to PUCCH resource number “n_(PUCCH)=6(=0+6)” in accordancewith Equation 1.

Meanwhile, the MTC coverage enhancement mode terminal uses a PUCCHresource corresponding to PUCCH resource number“n_(PUCCH_MTC)=30(=0+30)” in accordance with Equation 2.

More specifically, when configured with the normal mode, terminal 200(control section 213) adds offset value “N_(PUCCH) ⁽¹⁾” to index“n_(CCE)” of a CCE used for PDCCH to calculate the PUCCH resource to beactually used for an ACK/NACK signal. In addition, when configured withthe MTC coverage enhancement mode, terminal 200 adds offset value“N_(PUCCH_MTC) ⁽¹⁾” to index “n_(CCE)” of a CCE used for PDCCH tocalculate the PUCCH resource to be actually used for an ACK/NACK signal.However, offset value “N_(PUCCH) ⁽¹⁾” and offset value “N_(PUCCH_MTC)⁽¹⁾” are different.

Thus, in a case where the terminals of the two modes each transmit anACK/NACK signal in the same subframe, even if the CCE number associatedwith a PUCCH resource for transmitting an ACK/NACK signal from thenormal mode terminal and the CCE number associated with a PUCCH resourcefor transmitting an ACK/NACK signal from the MTC coverage enhancementmode terminal are both CCE #0, the PUCCH resources used by therespective terminals are different.

Stated differently, in a case where the terminals of the two modes eachtransmit an ACK/NACK signal in the same subframe, even if the CCEnumbers (smallest index) used for the corresponding PDCCH are the same,a PUCCH resource collision between the normal mode terminal and MTCcoverage enhancement mode terminal can be avoided.

As described above, according to Embodiment 1, PUCCH resources aredetermined for the normal mode and MTC coverage enhancement modeterminals using different offset values, respectively. As a result, thePUCCH resources available for the normal mode terminals are isolatedfrom the PUCCH resources available for the MTC coverage enhancement modeterminals. Thus, even when the CCEs occupied by PDCCH used for theassignment of downlink data corresponding to the ACK/NACK signals to betransmitted in the same subframe are the same, the PUCCH resources usedfor the ACK/NACK signals can be different. Thus, a PUCCH resourcecollision in transmission of the ACK/NACK signals can be avoided.

Moreover, as described above, a PUCCH resource collision is avoided bysetting different offset values to the normal mode and MTC coverageenhancement mode terminals, each of the offset values being used foridentifying a PUCCH resource number. Accordingly, it is not necessary toadd any restriction on PDCCH resource allocation. For this reason,Embodiment 1 does not involve any decrease in the utilization efficiencyof PUCCH resources or any increase in scheduling complexity.

According to Embodiment 1, a PUCCH resource collision between the normalmode terminal and MTC coverage enhancement mode terminal can be avoidedwithout any decrease in the utilization efficiency of PDCCH resources orany increase in scheduling complexity.

Moreover, the PUCCH resource allocation for the normal mode terminals(e.g., see Equation 1) has been already in practice in LTE systems. Forthis reason, in Embodiment 1, base station 100 additionally indicates,to terminal 200, only offset value “N_(PUCCH_MTC) ⁽¹⁾” usedindependently during the PUCCH resource allocation for the MTC coverageenhancement mode terminals. Thus, there is no major influence on theoperation of the current systems.

Embodiment 2

The basic configurations of a base station and a terminal according toEmbodiment 2 are similar to those in Embodiment 1, so that a descriptionwill be given below with reference to FIG. 8 (base station 100) and FIG.9 (terminal 200).

Hereinafter, as in Embodiment 1, a description will be given of a casewhere a normal mode terminal and an MTC coverage enhancement modeterminal coexist in a cell formed by base station 100.

Base station 100 according to Embodiment 2 indicates information on aPUCCH resource to each terminal 200 in advance. The information on aPUCCH resource is information on an offset value used for identifying aPUCCH resource number from a CCE number and a maximum number of PUCCHresources to be code-multiplexed per resource block (RB) placed in eachPUCCH region.

In Embodiment 2, the normal mode and MTC coverage enhancement modeterminals are set with a common offset value. However, the normal modeand MTC coverage enhancement mode terminals are different in theirassociations between CCE numbers and PUCCH resource numbers.

More specifically, the normal mode terminal determines, as in Embodiment1, resource number “n_(PUCCH)” of a PUCCH resource for transmission ofan ACK/NACK signal, in accordance with Equation 1, and determines an OCindex and cyclic shift value to be actually used.

Meanwhile, upon reception of downlink assignment control information(PDCCH or EPDCCH), the MTC coverage enhancement mode terminal determinesresource number “n_(PUCCH_MTC)” of a PUCCH resource for transmission ofan ACK/NACK signal for downlink data (PDSCH) indicated by thecorresponding assignment control information, using the followingequation.n _(PUCCH_MTC) =N _(PUCCH) ⁽¹⁾−1−n _(CCE)  (Equation 3)

In Equation 3, “N_(PUCCH) ⁽¹⁾” represents an offset value foridentifying a PUCCH resource number from a CCE number and is a valuealso included in Equation 1. Stated differently, offset value “N_(PUCCH)⁽¹⁾,” which is identical to “N_(PUCCH) ⁽¹⁾” for the normal modeterminals is set to the MTC coverage enhancement mode terminals. Forexample, base station 100 may indicate “N_(PUCCH) ⁽¹⁾” to terminal 200via a broadcast signal or higher layer signaling.

The MTC coverage enhancement mode terminal determines an OC index andcyclic shift value to be actually used, based on the determined PUCCHresource number “n_(PUCCH_MTC).”

More specifically, when configured with the normal mode, terminal 200(control section 213) adds offset value “N_(PUCCH) ⁽¹⁾” to index“n_(CCE)” of a CCE used for PDCCH to calculate the PUCCH resource to beactually used for an ACK/NACK signal. Meanwhile, when configured withthe MTC coverage enhancement mode, terminal 200 adds offset value“N_(PUCCH_MTC) ⁽¹⁾” to index “n_(CCE)” of a CCE used for PDCCH tocalculate the PUCCH resource to be actually used for an ACK/NACK signal.

FIG. 11 illustrates an example of PUCCH resources for the normal modeand MTC coverage enhancement mode terminals.

In FIG. 11 , 18 PUCCH resources are available among a maximum of 36PUCCH resources for each RB as in the case of FIG. 10 . In FIG. 11 , 54available PUCCH resources are assigned PUCCH resource numbers (#0 to#53), respectively, over three RBs.

In FIG. 11 , offset value “N_(PUCCH) ⁽¹⁾” for each terminal 200 is equalto 30.

More specifically, the normal mode terminal transmits an ACK/NACK signalusing a PUCCH resource of PUCCH resource number “n_(PUCCH)=n_(CCE)+30.”Meanwhile, the MTC coverage enhancement mode terminal transmits anACK/NACK signal using a PUCCH resource of PUCCH resource number“n_(PUCCH_MTC)=30−1−n_(CCE)(=29−n_(CCE)).”

Specifically, as illustrated in FIG. 11 , PUCCH resource numbers #29 and#30 serve as boundaries, and PUCCH resource numbers #30 and above areconfigured as a PUCCH resource region for the normal mode terminalswhile PUCCH resource numbers #29 and below are configured as a PUCCHregion for the MTC coverage enhancement mode terminals.

Accordingly, as illustrated in FIG. 11 , the different PUCCH resourceregions are configured for the normal mode and MTC coverage enhancementmode terminals, respectively. Stated differently, the PUCCH resourceregion is divided into a region for the normal mode terminals and aregion for the MTC coverage enhancement mode terminals by settingdifferent associations (i.e., Equations 1 and 3) for the normal mode andMTC coverage enhancement mode terminals, each of the associations beingused for identifying a PUCCH resource number from a CCE number.

Hereinafter, a description will be given of a case where the CCE numbercorresponding to the PUCCH resource used for an ACK/NACK signaltransmitted in the same subframe is CCE #0 (i.e., n_(CCE)=0) asillustrated in FIG. 5 , for example.

In this case, the normal mode terminal uses a PUCCH resourcecorresponding to PUCCH resource number “n_(PUCCH)=30(=0+30)” inaccordance with Equation 1.

Meanwhile, the MTC coverage enhancement mode terminal uses a PUCCHresource corresponding to PUCCH resource number“n_(PUCCH_MTC)=29(=29-0)” in accordance with Equation 3.

More specifically, in a case where the terminals of the two modes eachtransmit an ACK/NACK signal in the same subframe, even if the CCE numberassociated with a PUCCH resource for transmission of an ACK/NACK signalfrom the normal mode terminal and the CCE number associated with a PUCCHresource for transmission of an ACK/NACK signal from the MTC coverageenhancement mode terminal are both CCE #0, the PUCCH resources used bythe respective terminals are different.

Stated differently, in a case where the terminals of the two modes eachtransmit an ACK/NACK signal in the same subframe, even if the CCEnumbers (smallest index) used for the corresponding PDCCH are the same,a PUCCH resource collision between the normal mode terminal and MTCcoverage enhancement mode terminal can be avoided.

As described above, according to Embodiment 2, PUCCH resources aredetermined for the normal mode and MTC coverage enhancement modeterminals using different associations with CCEs. As a result, the PUCCHresources available for the normal mode terminals are isolated from thePUCCH resources available for the MTC coverage enhancement modeterminals. Thus, even when the CCEs occupied by PDCCH used for theassignment of downlink data corresponding to the ACK/NACK signals to betransmitted in the same subframe are the same, the PUCCH resources usedfor the ACK/NACK signals can be different. Thus, a PUCCH resourcecollision in transmission of the ACK/NACK signals can be avoided.

Moreover, as described above, a PUCCH resource collision is avoided bysetting different associations to the normal mode and MTC coverageenhancement mode terminals, each of the associations being used foridentifying a PUCCH resource number. Accordingly, it is not necessary toadd any restriction on PDCCH resource allocation. For this reason,Embodiment 2 does not involve any decrease in the utilization efficiencyof PUCCH resources or any increase in scheduling complexity.

According to Embodiment 2, a PUCCH resource collision between the normalmode terminal and MTC coverage enhancement mode terminal can be avoidedwithout any decrease in the utilization efficiency of PDCCH resources orany increase in scheduling complexity.

Moreover, the PUCCH resource allocation for the normal mode terminals(e.g., see Equation 1) has been already in practice in the LTE systems.In addition, the same parameter (offset value N_(PUUCH) ⁽¹⁾) as that forthe normal mode terminal is used for PUCCH resource allocation for theMTC coverage enhancement mode terminals. Thus, there is no parameter tobe added for the MTC coverage enhancement mode terminals. For thisreason, there is no influence on the operation of the current systems.

The associations for identifying PUCCH resource numbers from CCE numbersmay be reversed between the normal and MTC coverage enhancement modes.In other words, the normal mode terminal may determine a PUCCH resourcenumber using Equation 3, and the MTC coverage enhancement mode terminalmay determine a PUCCH resource number using Equation 1. In MTC,terminals are not likely to perform communication so often, so that itis unlikely that the MTC coverage enhancement mode terminals use thePUCCH region so often. Moreover, in uplink, the PUSCH (Physical UplinkShard Channel) region is placed in a center region of the system band,while the PUCCH regions are placed at the ends of the system band. Inaddition, the PUCCH resources (e.g., see FIG. 11 ) are assigned thePUCCH resource numbers in ascending order in a direction from the outerside to the inner side of the PUCCH regions. For this reason, the PUCCHregion for the MTC coverage enhancement mode terminals, which isassociated using Equation 1, and which is not used so often, is placedat the inner side of the frequency band in the uplink. Thus, the PUCCHregion can be contiguous with the uplink data frequency band. In thisconfiguration, when the PUCCH resources are not used by the MTC coverageenhancement mode terminals, these PUCCH resources can be used for uplinkdata (PUSCH). In addition, when the PUCCH region for the MTC coverageenhancement mode terminals is contiguous with the PUSCH region, aplurality of contiguous subcarriers can be collectively allocated to aspecific terminal to prevent an increase in Peak-to-Average Power Ratio(PAPR).

Embodiment 3

The basic configurations of a base station and a terminal in Embodiment3 are similar to those in Embodiment 1, so that a description will begiven with reference to FIG. 8 (base station 100) and FIG. 9 (terminal200).

Hereinafter, as in Embodiment 1, a description will be given of a casewhere a normal mode terminal and an MTC coverage enhancement modeterminal coexist in a cell formed by base station 100.

Base station 100 according to Embodiment 3 indicates information on aPUCCH resource to each terminal 200 in advance. The information on aPUCCH resource is information including a difference between cyclicshift values of available PUCCH resources adjacent to each other in asingle orthogonal sequence of PUCCH resources (e.g., see FIG. 3 ), and amaximum number of PUCCH resources to be code-multiplexed per RB to beplaced in each PUCCH region.

Moreover, the normal mode and MTC coverage enhancement mode terminalsare configured with different PUCCH resource regions, respectively.Hereinafter, a description will be given of a case where a PUCCHresource is indicated implicitly in association with a CCE number asPUCCH resource allocation for the MTC coverage enhancement modeterminals. For example, the normal mode and MTC coverage enhancementmode terminals may be configured with PUCCH resources by the method usedin Embodiment 1 or 2. In Embodiment 3, however, base station 100 mayexplicitly indicate a PUCCH resource to terminal 200 via higher layersignaling or the like as PUCCH resource allocation for the MTC coverageenhancement mode terminals.

In Embodiment 3, a difference between the cyclic shift values isindependently configured for the normal mode and MTC coverageenhancement mode terminals.

FIG. 12 illustrates an example of PUCCH resources for the normal modeand MTC coverage enhancement mode terminals according to Embodiment 3.FIG. 12 illustrates a total of 72 PUCCH resources of 2 RBs, and out ofthe 72 PUCCH resources, 12 PUCCH resources are secured for SPS/SR, 48PUCCH resources are secured for the normal mode terminals, and theremaining 12 PUCCH resources are secured for the MTC coverageenhancement mode terminals.

As described above, the PUCCH resources illustrated in FIG. 12 are eachdefined by a combination of an orthogonal code sequence (OC index) and acyclic shift value (cyclic shift index) of a ZAC sequence.

The normal mode terminal is configured with a cyclic shift valuedifference “Δ_(shift) ^(PUCCH)” between available resources adjacent toeach other in a single orthogonal code sequence that defines a PUCCHresource. For example, in FIG. 12 , the difference is set as Δ_(shift)^(PUCCH)=2. More specifically, among 12 cyclic shift values (cyclicshift index=0 to 11) of a single orthogonal code sequence, a PUCCHresource corresponding to every other cyclic shift value is available.Accordingly, 18 PUCCH resources are available for the normal modeterminals out of a maximum of 36 PUCCH resources for each RB (PRB(Physical RB)).

In FIG. 12 , upon reception of downlink assignment control information,the normal mode terminal may determine resource number “n_(PUCCH)” of aPUCCH resource for transmission of an ACK/NACK signal for the downlinkdata indicated by the corresponding downlink assignment controlinformation, in accordance with Equation 1 (provided that N_(PUCCH)⁽¹⁾=6).

In FIG. 12 , starting from PUCCH resource #0, 24 PUCCH resources ofPUCCH resource numbers #6 to #29 among the PUCCH resources assigned thenumbers corresponding to every other cyclic shift values in eachorthogonal sequence are the PUCCH resources available for the normalmode terminals.

Meanwhile, the MTC coverage enhancement mode terminal is configured witha cyclic shift value difference “Δ_(shift) ^(PUCCH_MTC)” betweenavailable resource adjacent to each other in a single orthogonal codesequence that defines PUCCH resources. For example, in FIG. 12 , thedifference is set as Δ_(shift) ^(PUCCH_MTC)=1. More specifically, as acyclic shift value difference between available PUCCH resources, the MTCcoverage enhancement mode terminal is configured with a parameterdifferent from a parameter configured for the normal mode terminal. Morespecifically, “Δ_(shift) ^(PUCCH_MTC)” is smaller than “Δ_(shift)^(PUCCH).”

More specifically, among 12 cyclic shift values (cyclic shift index=0 to11) of a single orthogonal code sequence, the PUCCH resourcescorresponding to all contiguous cyclic shift values are available forthe MTC coverage enhancement mode terminals.

In FIG. 12 , upon reception of downlink assignment control information,the MTC coverage enhancement mode terminal may determine resource number“n_(PUCCH_MTC)” of a PUCCH resource for transmission of an ACK/NACKsignal for the downlink data indicated by the corresponding downlinkassignment control information, in accordance with Equation 2 (providedthat N_(PUCCH_MTC) ⁽¹⁾=60).

In FIG. 12 , starting from PUCCH resource #0, 12 PUCCH resources ofPUCCH resource numbers #60 to #71 among the PUCCH resources assigned thenumbers corresponding to contiguous cyclic shift values in eachorthogonal sequence are the PUCCH resources available for the MTCcoverage enhancement mode terminals.

Note that, terminal 200 determines an OC index and cyclic shift value tobe actually used, based on a PUCCH resource number. The associationbetween PUCCH resource numbers, and OC indexes and cyclic shift valuesdepends on a difference between adjacent cyclic shift values.Accordingly, in Embodiment 3, the associations for identifying OCindexes and cyclic shift values to be actually used from PUCCH resourcenumbers are different for the normal mode and MTC coverage enhancementmode terminals. More specifically, the MTC coverage enhancement modeterminal may replace “Δ_(shift) ^(PUCCH)” in an equation representingthe association for identifying an OC index and cyclic shift value to beactually used, from a PUCCH resource number in the current systems (theequation is not illustrated) with Δ_(shift) ^(PUCCH_MTC) and operate.

In the current systems (e.g., 3GPP Release 11), PUCCH resources for thenormal mode terminals are reserved. When an MTC coverage enhancementmode terminal is present in the current systems, in addition to thePUCCH resources for the normal mode terminals, PUCCH resources for theMTC coverage enhancement mode terminal are additionally configured asillustrated in FIG. 12 .

As illustrated in FIG. 12 , a maximum number of codes that can bemultiplexed in each RB is identified by the number of available cyclicshift values among all possible cyclic shift values. More specifically,the maximum number of codes that can be multiplexed is identified inaccordance with which n-th cyclic shift value (where “n” is an integergreater than 0) is available as a PUCCH resource (i.e., Δshift^(PUCCH)and Δ_(shift) ^(PUCCH_MTC)).

In Embodiment 3, the maximum number of codes that can be multiplexed(i.e., difference between cyclic shift values) is configuredindependently for each of the normal mode and MTC coverage enhancementmode terminals. More specifically, among the combinations of theorthogonal code sequences and cyclic shift values defined as resourcesof a PUCCH resource group for the MTC coverage enhancement modeterminals, difference “Δ_(shift) ^(PUCCH_MTC)” between cyclic shiftvalues adjacent to each other in the same orthogonal sequence is smallerthan difference “Δ_(shift) ^(PUCCH)” between cyclic shift valuesadjacent to each other in the same orthogonal sequence among thecombinations of the orthogonal code sequences and cyclic shift valuesdefined as resources of a PUCCH resource group for the normal modeterminals.

For this reason, in the PUCCH resource region for the MTC coverageenhancement mode terminals, the proportion of available PUCCH resourcesfor each of the entire PUCCH resource regions becomes high as comparedwith the PUCCH resource region for the normal mode terminals. Morespecifically, as illustrated in FIG. 12 , 24 PUCCH resources areavailable among 48 PUCCH resources in the PUCCH resource region for thenormal mode terminals. In contrast to this, all 12 PUCCH resources areavailable in the PUCCH resource region for the MTC coverage enhancementmode terminals. Stated differently, the maximum number of codes that canbe multiplexed for the MTC coverage enhancement mode terminals becomesthe maximum.

More specifically, in Embodiment 3, setting the maximum number of codesthat can be multiplexed in PUCCH resources for the MTC coverageenhancement mode terminals to be greater than the maximum number ofcodes that can be multiplexed in PUCCH resources for the normal modeterminals as described above makes it possible to reduce the overheadfor PUCCH resources to the minimum level by increasing the number ofavailable PUCCH resources.

For example, in order to make 12 PUCCH resources available, 24 PUCCHresources need to be secured when Δ_(shift) ^(PUCCH_MTC)=2, but only 12PUCCH resources need to be secured when Δ_(shift) ^(PUCCH_MTC)=1. Thus,setting “Δ_(shift) ^(PUCCH_MTC)” to be smaller than “Δ_(shift) ^(PUCCH)”makes it possible to reduce the overhead for PUCCH resources to theminimum level as compared with the case where “Δ_(shift) ^(PUCCH_MTC)”is set equal to difference “Δ_(shift) ^(PUCCH)” between the cyclic shiftvalues configured for the normal mode terminals.

It is worth noting that, the PUCCH resources not used incode-multiplexing among the PUCCH resources of the same RB contribute toa reduction in inter-code interference because of the inter-codeinterference suppression effect brought about by code-spreading. Forexample, as illustrated in FIG. 12 , there are unused PUCCH resourcesbetween the available adjacent resources of PUCCH resources #6 to #29(PUCCH resources not used in code-multiplexing) among the PUCCHresources for the normal mode terminals, which in turn, makes acontribution to a suppression in inter-code interference.

In contrast to this, as illustrated in FIG. 12 , there is no PUCCHresource that is not used in code-multiplexing among the PUCCH resourcesfor the MTC coverage enhancement mode terminals.

However, taking the traffic characteristics of MTC into account, it isunlikely that the terminals in MTC perform communication so often. Inother words, the use frequency of PUCCH resources for the MTC coverageenhancement mode terminals is stochastically low. For this reason, evenif the maximum number of codes that can be multiplexed is increased inthe PUCCH resources for the MTC coverage enhancement mode terminals inthe same RB, the possibility of resources corresponding to cyclic shiftvalues adjacent to each other in the same sequence being usedsimultaneously is low because the number of terminals to becode-multiplexed simultaneously is few. More specifically, thepossibility of occurrence of inter-code interference due to thesimultaneous use of resources corresponding to the adjacent cyclic shiftvalues is low, so that it is unlikely that the propagationcharacteristics of ACK/NACK signals are reduced.

Moreover, taking the communication environment of MTC into account, itis likely that the coding rate of control information for the MTCcoverage enhancement mode terminals is set low, and that the number ofCCEs occupied by L1/L2 CCH forming the PDCCH is relatively large. Forthis reason, when a PUCCH resource number is implicitly indicated to theMTC coverage enhancement mode terminal by a CCE number, it is verylikely that the CCEs of adjacent numbers are used by the same terminal.Thus, it is less likely that the PUCCH resources of adjacent numbers(i.e., resources corresponding to adjacent cyclic shift values) aresimultaneously used.

As described above, even if the difference between adjacent cyclic shiftvalues is set low for the MTC coverage enhancement mode terminals ascompared with the normal mode terminals, there is practically noreduction in the performance of ACK/NACK signals due to an increase inthe maximum number of codes that can be multiplexed. The reason behindthis is that the probability of actual use in the PUCCH resource regionis low, where the maximum number of codes that can be multiplexed in thesame RB is increased.

As described above, according to Embodiment 3, the normal mode and MTCcoverage enhancement mode terminals are configured with PUCCH resourcesusing mutually different cyclic shift value differences (i.e., maximumnumber of codes that can be multiplexed). Thus, it is possible to reducethe overhead for the PUCCH resources to the minimum level in the systemwhere the normal mode and MTC coverage enhancement mode terminalscoexist.

In addition, the PUCCH resource allocation for the normal mode terminalshas been already in practice in the LTE systems. Thus, base station 100only needs to additionally indicate, to terminal 200, difference“Δ_(shift) ^(PUCCH_MTC)” between cyclic shift values independently usedduring PUCCH resource allocation for the MTC coverage enhancement modeterminals. Thus, there is no major influence on the operation of thecurrent systems.

In addition, according to Embodiment 3, a PUCCH resource collision intransmission of ACK/NACK signals can be avoided by setting differentPUCCH resources used for transmission of ACK/NACK signals to the normalmode and MTC coverage enhancement mode terminals.

Note that, Embodiment 3 has been described with a case where the normalmode terminals (i.e., terminals to which repetition is not applied) andthe MTC coverage enhancement mode terminals (i.e., terminals to whichrepetition is applied) are configured with PUCCH resources usingdifferent cyclic shift value differences (i.e., the maximum number ofcodes that can be multiplexed). Embodiment 3 is not limited to thiscase, however, and groups of terminals in the same cell (e.g., a groupof terminals served by macro base station and a group of terminalsserved by a remote antenna station in the same cell) may be configuredwith PUCCH resources using different cyclic shift value differences(i.e., the maximum number of codes that can be multiplexed).

Embodiment 4

As described above, the CCE numbers and PUCCH resource numbers areassociated with each other in one-to-one correspondence in the currentsystems. Stated differently, M CCEs are associated with M PUCCHresources (i.e., the number of CCEs and the number of PUCCH resourcesare the same), respectively. For example, in FIG. 12 , for the MTCcoverage enhancement mode terminals, CCE #0, CCE #1, CCE #2, and soforth are associated with PUCCH resource #60, PUCCH resource #61, PUCCHresource #62, and so forth, respectively.

Moreover, it is likely that a low coding rate is set for the controlinformation for the MTC coverage enhancement mode terminals for thepurpose of limiting the deterioration of error rate performance. Morespecifically, the number of CCEs occupied by L1/L2 CCH forming PDCCH forthe MTC coverage enhancement mode terminals is expected to be relativelylarge. For example, it is likely that a larger value (4, 8) amongpossible numbers of CCEs to be occupied (may be referred to as“aggregation level”) (e.g., 1, 2, 4, 8) is set for the MTC coverageenhancement mode terminals.

As described above, when L1/L2 CCH occupies a plurality of CCEs in PDCCHfor the MTC coverage enhancement mode terminal, the terminal transmitsan ACK/NACK signal using a PUCCH resource corresponding to one CCE (CCEhaving the smallest index) among the plurality of CCEs. Accordingly, thePUCCH resources corresponding to the CCEs other than the CCEcorresponding to the PUCCH resource used for transmission of theACK/NACK signal are not used and wasted. For example, in FIG. 12 , whenL1/L2 CCH forming the PDCCH for the MTC coverage enhancement modeterminal occupies four CCEs, CCE #0 to CCE #3, the terminal transmits anACK/NACK signal using only PUCCH resource #60, which corresponds to thesmallest index, CCE #0, among the four CCEs. As a result, the physicalresources of PUCCH resource #61 to PUCCH resource #63, which correspondto CCE #1 to CCE #3, are not used and thus wasted.

However, taking the traffic characteristics of MTC into account, it isunlikely that the terminals in MTC perform communication so often. Inother words, the use frequency of PUCCH resources for the MTC coverageenhancement mode terminals is stochastically low.

In this respect, in Embodiment 4, instead of associating M CCEs with MPUCCH resources in one to one correspondence for the MTC coverageenhancement mode terminals, M CCEs are associated with the number ofPUCCH resources smaller than M. In other words, one PUCCH resource isassociated with a plurality of CCEs for the MTC coverage enhancementmode terminals.

The basic configurations of a base station and a terminal in Embodiment4 are similar to those in Embodiment 1, so that a description will begiven with reference to FIG. 8 (base station 100) and FIG. 9 (terminal200).

Base station 100 and terminal 200 hold an association between CCEs andPUCCH resources according to Embodiment 4 in advance.

Hereinafter, Methods 1 and 2 for associating CCEs and PUCCH resourcesaccording to Embodiment 4 will be each described.

Note that, in Embodiment 4, as illustrated in FIG. 12 , for example, thenormal mode and MTC coverage enhancement mode terminals are configuredwith different PUCCH resource regions, respectively. For example, thenormal mode and MTC coverage enhancement mode terminals may beconfigured with PUCCH resources, using the same method as that ofEmbodiment 1 or 2. However, in Embodiment 4, base station 100 mayexplicitly indicate a PUCCH resource to terminal 200 via higher layersignaling or the like as PUCCH resource allocation for the MTC coverageenhancement mode terminals. Note that, a cyclic shift value differencebetween PUCCH resources available for the MTC coverage enhancement modeterminals is set to 1 (i.e., Δ_(shift) ^(PUCCH_MTC)=1) as in Embodiment3.

Hereinafter, a description will be given with focus on the PUCCHresources (#60 to #71) for the MTC coverage enhancement mode terminals.

<Method 1 (FIG. 13 )>

Method 1 is a method in which an association between CCE numbers andPUCCH resources is set based on a ratio of N to 1.

For example, FIG. 13 illustrates an example in which an associationbetween CCE numbers and PUCCH resources is set based on a ratio of N to1 where N=4.

As illustrated in FIG. 13 , four CCEs, CCE #0 to CCE #3, are associatedwith PUCCH resource #60, four CCEs, CCE #4 to CCE #7 are associated withPUCCH resource #61, and four CCEs, CCE #8 to CCE #11 are associated withPUCCH resource #62.

For example, when the CCE of the smallest index among the CCEs occupiedby L1/L2 CCH forming PDCCH intended for terminal 200 is any one of CCE#0 to CCE #3, the MTC coverage enhancement mode terminal transmits anACK/NACK signal using PUCCH resource #60. Likewise, when the CCE of thesmallest index among the CCEs allocated to the MTC coverage enhancementmode terminals is any one of CCE #4 to CCE #7, PUCCH resource #61 isused for transmission of the ACK/NACK signal, and when the CCE of thesmallest index is any one of CCE #8 to CCE #11, PUCCH resource #62 isused for transmission of the ACK/NACK signal.

For example, PUCCH resource number “n_(PUCCH_MTC)” used by the MTCcoverage enhancement mode terminals is determined in accordance with thefollowing equation.n _(PUCCH_MTC)=floor(n _(CCE) /N)+N _(PUCCH_MTC) ⁽¹⁾  (Equation 4)

In Equation 4, the function “floor(X)” represents a floor function thatreturns a largest integer not greater than X. In addition, “n_(CCE)”represents the smallest CCE number among the CCEs occupied by PDCCH, and“N” represents the number of CCEs associated with one PUCCH resource(e.g., N=4 in FIG. 13 ). In addition, “N_(PUCCH_MTC) ⁽¹⁾” represents anoffset value for the MTC coverage enhancement mode terminals. Forexample, N_(PUCCH_MTC) ⁽¹⁾=60 in FIG. 13 .

According to Method 1, the PUCCH resource region to be secured for theMTC coverage enhancement mode terminals is reduced to 1/N compared withthe case where the CCE numbers and PUCCH resource numbers are associatedwith each other in one to one correspondence. More specifically, whenthe CCE numbers and PUCCH resource numbers are associated with eachother in one to one correspondence, 12 PUCCH resources need to besecured for 12 CCEs, but Method 1 requires only 3 PUCCH resources to besecured for 12 CCEs in the case of FIG. 13 (where N=4).

<Method 2>

Method 2 is a method in which the number of CCEs to be associated withone PUCCH resource is set to a value that can be taken as the number ofoccupied CCEs (aggregation level).

For example, let us suppose that the number of CCEs occupied for the MTCcoverage enhancement mode terminals is set to N (>1) in Method 2.

FIG. 14 illustrates an example of an association between the CCE numbersand PUCCH resource numbers when N=4, for example.

As illustrated in FIG. 14 , four CCEs, CCE #0 to CCE #3 are associatedwith PUCCH resource #60, four CCEs, CCE #4 to CCE #7 are associated withPUCCH resource #61, and four CCEs, CCE #8 to CCE #11 are associated withPUCCH resource #62. More specifically, one PUCCH resource is associatedwith every set of N occupied CCEs.

The MTC coverage enhancement mode terminal is allocated CCEs in units offour CCEs as illustrated in FIG. 14 . For example, when the CCEsoccupied by L1/L2 CCH forming PDCCH intended for terminal 200 are CCE #0to CCE #3, the MTC coverage enhancement mode terminal transmits anACK/NACK signal using PUCCH resource #60. Likewise, when the MTCcoverage enhancement mode terminal is allocated CCE #4 to CCE #7, theMTC coverage enhancement mode terminal transmits the ACK/NACK signalusing PUCCH resource #61, and when the MTC coverage enhancement modeterminal is allocated CCE #8 to CCE #11, the MTC coverage enhancementmode terminal transmits the ACK/NACK signal using PUCCH resource #62.

For example, PUCCH resource number “n_(PUCCH_MTC)” is determined inaccordance with the following equation.n _(PUCCH_MTC) =n _(CCE) /N+N _(PUCCH_MTC) ⁽¹⁾  (Equation 5)

In Equation 5, “n_(CCE)” represents the smallest CCE number among theCCEs occupied by PDCCH, and “N” represents the number of CCEs occupiedfor the MTC coverage enhancement mode terminals (e.g., N=4 in FIG. 14 ).In addition, “N_(PUCCH_MTC) ⁽¹⁾” represents an offset value for the MTCcoverage enhancement mode terminals. For example, N_(PUCCH_MTC) ⁽¹⁾=60in FIG. 14 .

According to Method 2, the PUCCH resource region to be secured for theMTC coverage enhancement mode terminals is reduced to 1/N compared withthe case where the CCE numbers and PUCCH resource numbers are associatedwith each other in one to one correspondence. More specifically, whenCCE numbers are PUCCH resource numbers are associated in one to onecorrespondence, 12 PUCCH resources need to be secured for 12 CCEs, butMethod 2 requires only 3 PUCCH resources to be secured for 12 CCEs inthe case of FIG. 14 (where N=4).

Moreover, each PUCCH resource is associated with CCEs in units of CCEsoccupied for each terminal, so that there is no chance that N CCEsassociated with one PUCCH resource are simultaneously used by aplurality of terminals.

Methods 1 and 2 have been described thus far.

As described above, in Embodiment 4, one PUCCH resource is associatedwith a plurality of CCEs for the MTC coverage enhancement mode terminal.Thus, it is possible to avoid an increase in resources to be reserved asa PUCCH resource for the MTC coverage enhancement mode terminals.Accordingly, even in a system in which an MTC coverage enhancement modeterminal exists (i.e., case where a PUCCH resource for the MTC coverageenhancement mode terminal is additionally configured), an increase inthe overhead for PUCCH resources can be avoided.

In addition, according to Embodiment 4, a PUCCH resource collision intransmission of ACK/NACK signals can be avoided by setting differentPUCCH resources used for transmission of the ACK/NACK signals to thenormal mode and MTC coverage enhancement mode terminals.

Embodiment 5

Implicitly indicating a PUCCH resource number in association with a CCEnumber to the MTC coverage enhancement mode terminals in the same manneras the current systems may cause a PUCCH resource collision becauseACK/NACK signals may be simultaneously transmitted using the same PUCCHresource from the terminals when a terminal configured with PDCCH andPUCCH of different repetition levels exists.

FIG. 15 illustrates an example of the case where PUCCH resources for theMTC coverage enhancement mode terminals collide with each other. In FIG.15 , “N_(PDCCH)” and “N_(PDSCH)” represent the repetition levels ofPDCCH and PDSCH of each of terminal 1 (UE #1) and terminal 2 (UE #2). Inaddition, “N_(PUCCH)+α_(PUCCH)” represents the repetition level of PUCCHof terminal 1, and “N_(PUCCH)” represents the repetition level of PUCCHof terminal 2. More specifically, “N_(PDCCH)” and “N_(PDSCH)” ofterminal 1 are identical to those of terminal 2, but the repetitionlevel of PUCCH of terminal 1 is greater than that of terminal 2 by“α_(PUCCH)”

In FIG. 15 , PDCCH is transmitted to terminal 1 using CCE #0 to CCE #3.Meanwhile, PDCCH is transmitted to terminal 2 using CCE #0 to CCE #3 inthe subframe subsequent to the subframe in which the transmission ofPDCCH to terminal 1 has been completed. Stated differently, bothterminals 1 and 2 transmit an ACK/NACK signal using a PUCCH resourceassociated with CCE #0.

As illustrated in FIG. 15 , terminal 1 transmits an ACK/NACK signal over“N_(PUCCH)+α_(PUCCH)” subframes, while terminal 2 transmits an ACK/NACKsignal on “N_(PUCCH)” in the subframe subsequent to the subframe inwhich terminal 1 has transmitted an ACK/NACK signal on “N_(PUCCH).” Forthis reason, as illustrated in FIG. 15 , the PUCCH resources for theterminals collide with each other in the subframe corresponding to the“α_(PUCCH)” subframe of the last half of PUCCH repetition of terminal 1and the “α_(PUCCH)” subframe of the top half of PUCCH repetition ofterminal 2.

In this respect, in Embodiment 5, a method for avoiding a PUCCH resourcecollision in transmission of ACK/NACK signals from the MTC coverageenhancement mode terminals will be described.

The basic configurations of a base station and a terminal in Embodiment5 are similar to those in Embodiment 1, so that a description will begiven with reference to FIG. 8 (base station 100) and FIG. 9 (terminal200).

Specifically, when the repetition levels of PDCCH and PUCCH aredifferent, terminal 200 (MTC coverage enhancement mode terminal)transmits an ACK/NACK signal using a PUCCH resource implicitly indicatedin association with a CCE number (i.e., smallest CCE number) for thenumber of subframes corresponding to the repetition level of PDCCHduring the PUCCH repetition.

Meanwhile, terminal 200 transmits an ACK/NACK signal using an explicitlyallocated PUCCH resource in a subframe exceeding the repetition level ofPDCCH. The PUCCH resource is previously indicated to terminal 200 bybase station 100.

FIG. 16 illustrates the transmission timing of each channel inEmbodiment 5. In FIG. 16 , “N_(PDCCH)” and “N_(PDSCH)” represent therepetition levels of PDCCH and PDSCH of each of terminal 1 (UE #1) andterminal 2 (UE #2) as in the case of FIG. 15 . In addition,“N_(PUCCH)+α_(PUCCH)” represents the repetition level of PUCCH ofterminal 1, and “N_(PUCCH)” represents the repetition level of PUCCH ofterminal 2. Note that, “N_(PUCCH)” and “N_(PDCCH)” are the same in FIG.16 .

Moreover, in FIG. 16 , PDCCH is transmitted to terminal 1 using CCE #0to CCE #3. Meanwhile, PDCCH is transmitted to terminal 2 using CCE #0 toCCE #3 in the subframe subsequent to the subframe in which thetransmission of PDCCH to terminal 1 has been completed.

In this case, as illustrated in FIG. 16 , terminal 1 transmits anACK/NACK signal using a PUCCH resource associated with CCE #0 of thesmallest index among the CCEs used for PDCCH, for the number ofN_(PUCCH) subframes corresponding to the number of “N_(PDCCH)” subframesamong “N_(PUCCH)+α_(PUCCH)” subframes during PUCCH repetition.

Meanwhile, terminal 1 transmits an ACK/NACK signal using an explicitlyindicated PUCCH resource in an “α_(PUCCH)” subframe exceeding the“N_(PUCCH)” subframe among “N_(PUCCH)+α_(PUCCH)” subframes.

In addition, as illustrated in FIG. 16 , terminal 2 transmits anACK/NACK signal using a PUCCH resource associated with CCE #0 of thesmallest index among the CCEs used for PDCCH in the “N_(PUCCH)” subframesubsequent to the “N_(PUCCH)” subframe in which terminal 1 hastransmitted an ACK/NACK signal, during the PUCCH repetition.

More specifically, in FIG. 16 , terminals 1 and 2 use mutually differentPUCCH resources in the subframe corresponding to the “α_(PUCCH)”subframe of the last half of PUCCH repetition of terminal 1 and the“N_(PUCCH)” subframe of the top half of PUCCH repetition of terminal 2.As a result, no PUCCH resource collision occurs between terminals 1 and2.

As described above, among a plurality of subframes used for repeatedlytransmitting an ACK/NACK signal, terminal 200 transmits an ACK/NACKsignal using a PUCCH resource associated with a CCE used in PDCCH amongthe PUCCH resources for the MTC coverage enhancement mode terminals, ina subframe not greater than the repetition level of PDCCH, and transmitsan ACK/NACK signal using any of previously configured PUCCH resources,in a subframe exceeding the repetition level of PDCCH.

In this manner, in a case where an MTC coverage enhancement modeterminal configured with PDCCH and PUCCH of different repetition levelsis present, even if there occurs a subframe in which ACK/NAC signals aresimultaneously transmitted from the MTC coverage enhancement modeterminals to which PDCCH has been transmitted using the same CCE, aPUCCH resource collision in transmission of the ACK/NACK signals fromthe terminals can be avoided.

It should be noted that, Embodiment 5 may be combined with the operationof Embodiments 1 to 4. In other words, Embodiment 5 may be applied tothe method for avoiding a PUCCH resource collision between the MTCcoverage enhancement mode terminals, and any one of Embodiments 1 to 4may be applied to the method for avoiding a PUCCH resource collisionbetween the normal mode terminal and MTC coverage enhancement modeterminal.

Embodiment 6

Embodiment 5 has been described with respect to a terminal configuredwith PDCCH and PUCCH of different repetition levels. Embodiment 6, onthe other hand, will be described with respect to a case where eachterminal is configured with PDCCH and PUCCH of the same repetitionlevels, but the repetition levels of PDCCH and PUCCH configured for theterminals are different.

In this case, implicitly indicating a PUCCH resource number inassociation with a CCE number to the MTC coverage enhancement modeterminals in the same manner as the current systems may cause a PUCCHresource collision because ACK/NACK signals may be simultaneouslytransmitted using the same PUCCH resource from the terminals.

FIG. 17 illustrates an example of a case where PUCCH resources used bythe MTC coverage enhancement mode terminals collide with each other. InFIG. 17 , the repetition levels of PDCCH, PDSCH, and PUCCH for terminal1 (UE #1) are 8, and the repetition levels of PDCCH, PDSCH, and PUCCHfor terminal 2 (UE #2) are 4.

In FIG. 17 , PDCCH is transmitted to terminal 1 using CCE #0 to CCE #3.Meanwhile, PDCCH is transmitted to terminal 2 using CCE #0 to CCE #3 inthe subframe subsequent to the subframe in which the transmission ofPDCCH to terminal 1 has been completed. Stated differently, bothterminals 1 and 2 transmit an ACK/NACK signal using a PUCCH resourceassociated with CCE #0.

As illustrated in FIG. 17 , terminal 1 receives PDCCH over 8 subframesand receives PDSCH over the next 8 subframes. Meanwhile, terminal 2receives PDCCH over 4 subframes subsequent to the subframe in whichterminal 1 has completed reception of PDCCH and receives PDSCH over thenext 4 subframes. More specifically, terminals 1 and 2 complete thereception of PDSCH at the same timing (or start transmission of anACK/NACK signal at the same timing).

In this case, terminal 1 transmits an ACK/NACK signal over 8 subframes,and terminal 2 transmits an ACK/NACK signal over 4 subframes at the sametiming. As a result, as illustrated in FIG. 17 , a PUCCH resourcecollision occurs in the subframes corresponding to the 4 subframes ofthe top half of PUCCH repetition of terminal 1 and the 4 subframescorresponding to the whole subframes of PUCCH repetition of terminal 2.

In this respect, Embodiment 6 will be described with respect to a methodfor avoiding a PUCCH resource collision in transmission of ACK/NACKsignals from the MTC coverage enhancement mode terminals configured withdifferent repetition levels.

The basic configurations of a base station and a terminal in Embodiment6 are similar to those in Embodiment 1, so that a description will begiven with reference to FIG. 8 (base station 100) and FIG. 9 (terminal200).

Specifically, terminal 200 (MTC coverage enhancement mode terminal)transmits an ACK/NACK signal using a PUCCH resource implicitly indicatedin association with a CCE number used in transmission of PDCCH (i.e.,smallest CCE number) during PUCCH repetition. Terminal 200, however,transmits an ACK/NACK signal using a PUCCH resource identified by usinga different offset value for each configured repetition level.

For example, PUCCH resource number “n_(PUCCH_MTC_4)” used when therepetition level is 4, and PUCCH resource number “n_(PUCCH_MTC_8)” usedwhen the repetition level is 8 are determined in accordance with thefollowing equations.n _(PUCCH_MTC_8) =n _(CCE) +N _(PUCCH_MTC_8) ⁽¹⁾  (Equation 6)n _(PUCCH_MTC_4) =n _(CCE) +N _(PUCCH_MTC_4) ⁽¹⁾  (Equation 7)

In Equations 6 and 7, “n_(CCE)” represents the CCE number (integer notless than 0) of a CCE occupied by PDCCH. In addition, “N_(PUCCH_MTC_8)⁽¹⁾” represents an offset value for identifying the PUCCH resourcenumber from the CCE number when the repetition level is 8, while“N_(PUCCH_MTC_4) ⁽¹⁾” represents an offset value for identifying thePUCCH resource number from the CCE number when the repetition level is 4in Equations 6 and 7.

Different values are set to N_(PUCCH_MTC_4) ⁽¹⁾ and N_(PUCCH_MTC_8) ⁽¹⁾,respectively. In other words, PUCCH resources available for terminal 200are at least divided into PUCCH resources used when the repetition levelis 4 and PUCCH resources used when the repetition level is 8. Morespecifically, a PUCCH resource group available for terminal 200 includesa plurality of sub-resource groups for the respective repetition levelsfor an ACK/NACK signal.

Note that, hereinafter, a description will be given of a case where therepetition levels are 4 and 8, but the repetition levels are not limitedto 4 or 8, and when a different value is used, an offset value isconfigured for the value in the same manner.

FIG. 18 illustrates the transmission timing of each channel inEmbodiment 6. In FIG. 18 , the repetition levels of PDCCH, PDSCH, andPUCCH for terminal 1 (UE #1) are 8, and the repetition levels of PDCCH,PDSCH, and PUCCH for terminal 2 (UE #2) are 4 as in the case of FIG. 17. In addition, in FIG. 18 , PDCCH is transmitted to terminal 1 using CCE#0 to CCE #3. Meanwhile, PDCCH is transmitted to terminal 2 using CCE #0to CCE #3 in the subframe subsequent to the subframe in which thetransmission of PDCCH to terminal 1 has been completed.

In this case, as illustrated in FIG. 18 , terminal 1 transmits anACK/NACK signal using a PUCCH resource corresponding ton_(PUCCH_MTC_8)=n_(CCE)±N_(PUCCH_MTC_8) ⁽¹⁾ in accordance with Equation6 during PUCCH repetition, while terminal 2 transmits an ACK/NACK signalusing a PUCCH resource corresponding ton_(PUCCH_MTC_4)=n_(CCE)+N_(PUCCH_MTC_4) ⁽¹⁾ in accordance with Equation7 during PUCCH repetition.

As described above, N_(PUCCH_MTC_4) ⁽¹⁾ and N_(PUCCH_MTC_8) ⁽¹⁾ aredifferent from each other. Thus, as illustrated in FIG. 18 , terminals 1and 2 use mutually different PUCCH resources in the subframescorresponding to the 4 subframes of the top half of PUCCH repetition ofterminal 1 and the 4 subframes corresponding to the whole subframes ofPUCCH repetition of terminal 2. As a result, no PUCCH resource collisionoccurs between terminals 1 and 2.

In this manner, even if there occurs a subframe in which ACK/NAC signalsare simultaneously transmitted from the MTC coverage enhancement modeterminals which are configured with mutually different repetition levelsand to which PDCCH has been transmitted using the same CCE, a PUCCHresource collision in transmission of the ACK/NACK signals from theterminals can be avoided.

It should be noted that, Embodiment 6 may be combined with the operationof Embodiments 1 to 4. In other words, Embodiment 6 may be applied tothe method for avoiding a PUCCH resource collision between the MTCcoverage enhancement mode terminals, and any one of Embodiments 1 to 4may be applied to the method for avoiding a PUCCH resource collisionbetween the normal mode terminal and MTC coverage enhancement modeterminal.

Each embodiment of the present disclosure has been described thus far.

Note that, although each embodiment has been described with an examplein which an aspect of this disclosure is configured with hardware by wayof example, the present disclosure may also be realized by software inconcert with hardware.

In addition, the functional blocks used in the description of eachembodiment are typically implemented as LSI devices, which areintegrated circuits. The functional blocks may be formed as individualchips, or a part or all of the functional blocks may be integrated intoa single chip. The term “LSI” is used herein, but the terms “IC,”“system LSI,” “super LSI” or “ultra LSI” may be used as well dependingon the level of integration.

In addition, the circuit integration is not limited to LSI and may beachieved by dedicated circuitry or a general-purpose processor otherthan an LSI. After fabrication of LSI, a field programmable gate array(FPGA), which is programmable, or a reconfigurable processor whichallows reconfiguration of connections and settings of circuit cells inLSI may be used.

Should a circuit integration technology replacing LSI appear as a resultof advancements in semiconductor technology or other technologiesderived from the technology, the functional blocks could be integratedusing such a technology. Another possibility is the application ofbiotechnology, for example.

A terminal according to the present disclosure includes: a receivingsection that receives control information indicating assignment ofdownlink data, and the downlink data; a control section that determinesa resource used for a response signal for the downlink data, based onthe control information; and a transmitting section that transmits theresponse signal using the determined resource, in which: thetransmitting section transmits the response signal using a resource in afirst resource group when the terminal is a first terminal to whichrepetition transmission for the control information, the downlink data,and the response signal is applied; and the transmitting sectiontransmits the response signal using a resource in a second resourcegroup when the terminal is a second terminal to which the repetitiontransmission is not applied, the second resource group being differentfrom the first resource group.

In the terminal according to this disclosure: the control sectioncalculates a resource used for the response signal in the first resourcegroup by adding a first offset value to an index of a control channelelement (CCE) used for the control information; the control sectioncalculates a resource used for the response signal in the secondresource group by adding a second offset value to the index of the CCEused for the control information; and the first offset value and thesecond offset value are different.

In the terminal according to the present disclosure: the control sectioncalculates a resource used for the response signal in the first resourcegroup by adding an offset value to an index of a control channel element(CCE) used for the control information; and the control sectioncalculates a resource used for the response signal in the secondresource group by subtracting the index of the CCE used for the controlinformation from the offset value.

In the terminal according to the present disclosure: the first resourcegroup and the second resource group each include resources respectivelydefined by combinations each being of an orthogonal code sequence and acyclic shift value; and a difference between adjacent cyclic shiftvalues in a single orthogonal code sequence among the combinationsdefined as the resources of the first resource group is smaller than adifference between adjacent cyclic shift values in a single orthogonalcode sequence among the combinations defined as the resources of thesecond resource group.

In the terminal according to the present disclosure, each resource inthe first resource group is associated with a plurality of controlchannel elements (CCE) used for the control information.

In the terminal according to the present disclosure, a number of theplurality of CCEs is a number of CCEs occupied by the controlinformation.

In the terminal according to the present disclosure: the transmissionsection transmits the response signal using a resource associated with acontrol channel element (CCE) used for the control information in thefirst resource group for a number of subframes corresponding to a numberof repetitions for the control information among a plurality ofsubframes in which the repetition transmission for the response signalis performed; and the transmitting section transmits the response signalusing a predetermined resource in a subframe exceeding the number ofrepetitions for the control information among the plurality of subframesin which the repetition transmission for the response signal isperformed.

In the terminal according to the present disclosure, the first resourcegroup includes a plurality of sub-resource groups each configured for acorresponding number of repetitions for the response signal.

A base station according to this disclosure includes: a transmittingsection that transmits control information indicating assignment ofdownlink data, and the downlink data; a control section that determinesa resource used for a response signal for the downlink data, based onthe control information; and a receiving section that receives theresponse signal using the determined resource, in which: the receivingsection receives, using a resource in a first resource group, theresponse signal transmitted from a first terminal to which repetitiontransmission for the control information, the downlink data, and theresponse signal is applied; and the receiving section receives, using aresource in a second resource group, the response signal transmittedfrom a second terminal to which the repetition transmission is notapplied, the second resource group being different from the firstresource group.

A transmitting method according to this disclosure includes: receivingcontrol information indicating assignment of downlink data, and thedownlink data; determining a resource used for a response signal for thedownlink data, based on the control information;

and transmitting the response signal using the determined resource, inwhich: in the transmitting of the response signal, the response signalis transmitted using a resource in a first resource group from a firstterminal to which repetition transmission for the control information,the downlink data, and the response signal is applied; and in thetransmitting of the response signal, the response signal is transmittedusing a resource in a second resource group from a second terminal towhich the repetition transmission is not applied, the second resourcegroup being different from the first resource group.

A receiving method according to this disclosure includes: transmittingcontrol information indicating assignment of downlink data, and thedownlink data; determining a resource used for a response signal for thedownlink data, based on the control information; and receiving theresponse signal using the determined resource, in which: in thereceiving of the response signal, the response signal transmitted from afirst terminal is received using a resource in a first resource group,the first terminal being a terminal to which repetition transmission forthe control information, the downlink data, and the response signal isapplied; and in the receiving of the response signal, the responsesignal transmitted from a second terminal is received using a resourcein a second resource group that is different from the first resourcegroup, the second terminal being a terminal to which the repetitiontransmission is not applied.

INDUSTRIAL APPLICABILITY

An aspect of the present disclosure is useful in mobile communicationsystems.

REFERENCE SIGNS LIST

-   100 Base station-   200 Terminal-   101, 213 Control section-   102 Control signal generating section-   103 Control signal coding section-   104 Control signal modulation section-   105 Broadcast signal generating section-   106 Data coding section-   107 Retransmission control section-   108 Data modulation section-   109 Signal assignment section-   110, 218 IFFT section-   111, 219 CP adding section-   112, 220 Transmitting section-   113 Antenna-   114, 202 Receiving section-   115, 203 CP removing section-   116 PUCCH extracting section-   117 Sequence control section-   118 Despreading section-   119 Correlation processing section-   120, 209 Determination section-   204 FFT section-   205 Extracting section-   206 Broadcast signal receiving section-   207 Control signal demodulation section-   208 Control signal decoding section-   210 Data demodulation section-   211 Data decoding section-   212 CRC section-   214 ACK/NACK generating section-   215 Modulation section-   216 Primary-spreading section-   217 Secondary-spreading section

The invention claimed is:
 1. A terminal comprising: a receiver, which,in operation, receives downlink control information and downlink data;circuitry, which, in operation, determines, based on the downlinkcontrol information and an offset, a physical uplink control channel(PUCCH) resource used for transmission of a response signal for thedownlink data; and a transmitter, which, in operation, transmits theresponse signal using the determined PUCCH resource, wherein: a firstoffset is used as the offset when the terminal is configured in acoverage enhancement mode, in which the response signal is allowed to betransmitted repeatedly for one of plural repetition levels in aplurality of subframes, where the first offset is configured for each ofthe plural repetition levels; and the first offset is different from asecond offset, which is used when the terminal is not configured in thecoverage enhancement mode.
 2. The terminal according to claim 1, whereinthe receiver, in operation, receives the downlink control informationtransmitted across a plurality of subframes in the coverage enhancementmode.
 3. The terminal according to claim 1, wherein: a combination ofone of orthogonal sequences and one of cyclic shifts is determined froman association of the PUCCH resource with the combination; and a firstassociation in the coverage enhancement mode is different from a secondassociation, which is used when the terminal is not configured in thecoverage enhancement mode.
 4. The terminal according to claim 3, whereinthe association is based on a difference between adjacent cyclic shiftsthat are combined with one of the orthogonal sequences, and thedifference of the first association in the coverage enhancement mode isconfigured independently of the difference of the second association,which is used when the terminal is not configured in the coverageenhancement mode.
 5. The terminal according to claim 1, wherein thetransmitter, in operation, transmits the response signal repeatedlyspanning a plurality of subframes in the coverage enhancement mode. 6.The terminal according to claim 1, wherein the transmitter, inoperation, transmits the response signal k subframes after the lastsubframe in which the downlink data is received in the coverageenhancement mode, where k is an integer.
 7. The terminal according toclaim 1, wherein the first offset is specific to the terminal, and thesecond offset is common in a cell.
 8. The terminal according to claim 1,wherein the first offset is common to terminals configured in thecoverage enhancement mode.
 9. The terminal according to claim 1, whereinthe receiver, in operation, receives at least one of the first offsetand the second offset, which is configured by a higher layer.
 10. Theterminal according to claim 1, wherein the receiver, in operation,receives the downlink data transmitted repeatedly spanning a pluralityof subframes in the coverage enhancement mode.
 11. A communicationmethod comprising: receiving downlink control information and downlinkdata; determining, based on the downlink control information and anoffset, a physical uplink control channel (PUCCH) resource used fortransmission of a response signal for the downlink data; andtransmitting the response signal using the determined PUCCH resource,wherein: a first offset is used as the offset when a terminal isconfigured in a coverage enhancement mode, in which the response signalis allowed to be transmitted repeatedly for one of plural repetitionlevels in a plurality of subframes, where the first offset is configuredfor each of the plural repetition levels; and the first offset isdifferent from a second offset, which is used when the terminal is notconfigured in the coverage enhancement mode.
 12. The communicationmethod according to claim 11, wherein the receiving includes receivingthe downlink control information transmitted across a plurality ofsubframes in the coverage enhancement mode.
 13. The communication methodaccording to claim 11, wherein: a combination of one of orthogonalsequences and one of cyclic shifts is determined from an association ofthe PUCCH resource with the combination; and a first association in thecoverage enhancement mode is different from a second association, whichis used when the terminal is not configured in the coverage enhancementmode.
 14. The communication method according to claim 13, wherein theassociation is based on a difference between adjacent cyclic shifts thatare combined with one of the orthogonal sequences, and the difference ofthe first association in the coverage enhancement mode is configuredindependently of the difference of the second association, which is usedwhen the terminal is not configured in the coverage enhancement mode.15. The communication method according to claim 11, wherein thetransmitting includes transmitting the response signal repeatedlyspanning a plurality of subframes in the coverage enhancement mode. 16.The communication method according to claim 11, wherein the transmittingincludes transmitting the response signal k subframes after the lastsubframe in which the downlink data is received in the coverageenhancement mode, where k is an integer.
 17. The communication methodaccording to claim 11, wherein the first offset is specific to theterminal, and the second offset is common in a cell.
 18. Thecommunication method according to claim 11, wherein the first offset iscommon to terminals configured in the coverage enhancement mode.
 19. Thecommunication method according to claim 11 comprising receiving at leastone of the first offset and the second offset, which is configured by ahigher layer.
 20. The communication method according to claim 11comprising receiving the downlink data transmitted repeatedly spanning aplurality of subframes in the coverage enhancement mode.